Identity-coded surface with coded marks

ABSTRACT

A region defined in relation to a surface, and a method for defining such a region; coded data being disposed within the region, the coded data being indicative of an identity of the region; in one embodiment, the coded data comprising a plurality of tags which substantially cover the region, the tags being usable to uniquely identify the region or at least distinguish it from other regions defined in relation to the surface.

CO-PENDING APPLICATIONS

[0001] Various methods, systems and apparatus relating to the presentinvention are disclosed in the following co-pending applications filedby the applicant or assignee of the present invention simultaneouslywith the present application:

[0002] NPA001US, NPA002US, NPA003US, NPA004US, NPA005US, NPA006US,NPA007US, NPA008US, NPA009US, NPA010US, NPA012US, NPA016US, NPA017US,NPA018US, NPA019US, NPA020US, NPA021US, NPA030US, NPA035US, NPA048US,NPA050US, NPA051US, NPA052US, NPA075US, NPB001US, NPB002US, NPK002US,NPK003US, NPK004US, NPK005US, NPK007US, NPM001US, NPM002US, NPM003US,NPM004US, NPN001US, NPN002US, NPN003US, NPP001US, NPP002US, NPP003US,NPP005US, NPP006US, NPP007US, NPP008US, NPP016US, NPP017US, NPP018US,NPP019US, NPS001US, NPS003US, NPS020US, NPT001US, NPT002US, NPT003US,NPT004US, NPX001US, NPX003US, NPX008US, NPX011US, NPX014US, NPX016US,NPX020US, NPX022US, IJ52US, IJM52US, MJ10US, MJ11US, MJ12US, MJ13US,MJ14US, MJ15US, MJ34US, MJ47US, MJ52US, MJ58US, MJ62US, MJ63US, PAK04US,PAK05US, PAK06US, PAK07US, PAK08US, PEC01US, PEC02US.

[0003] The disclosures of these co-pending applications are incorporatedherein by cross-reference. Each application is temporarily identified byits docket number. This will be replaced by the corresponding USSN whenavailable.

FIELD OF INVENTION

[0004] The present invention relates generally to a method of defining aregion in relation to a surface, and to a region so defined.

[0005] The invention has been developed primarily to provide the basisfor a surface-based interface which allows a user to input and interactwith information via a network, and to obtain interactive printed matteron demand via high-speed networked color printers. Although theinvention will largely be described herein with reference to this use,it will be appreciated that the invention is not limited to use in thisfield.

BACKGROUND

[0006] Presently, the majority of forms for accepting input from a userare either printed on paper or displayed on a computer screen. With apaper-based form, the user writes information on the form by hand,usually in spaces or boxes provided adjacent printed questions orinstructions. The information is later keyed into a computer system foronline storage processing and storage. With a screen-based form, theuser enters information into the form via a computer keyboard. Both ofthese approaches have disadvantages. The screen-based approach isconvenient to the form recipient, but requires that the user have accessto a computer system. By contrast, the paper-based approach onlyrequires the user to apply pen to paper, but requires the form recipientto wait for manual delivery of the form and perform data entry of itscontent.

OBJECT

[0007] It is an object of the present invention to combine advantages ofpaper-based forms and immediate online information capture.

SUMMARY OF INVENTION

[0008] In a first aspect of the invention, there is provided a regiondefined in relation to a surface, coded data being disposed within theregion, wherein the coded data includes identity data for identifyingthe region.

[0009] Preferably, the coded data takes the form of at least one tag. Ina preferred form, there are a plurality of tags that substantially fillthe region.

[0010] Preferably, each of the tags within a region are identical toeach other, but are distinct from tags in a plurality of other regions.

[0011] In one preferred embodiment, the tags are positionedstochastically within the region. In an alternative preferment, the tagsare positioned in a regular array within the region.

[0012] In a second aspect of the invention, there is provided a methodof producing a surface having a region, the method including the stepsof:

[0013] (a) defining coded data, the coded data being indicative of:

[0014] a region identity associated with the region; and

[0015] a plurality of points within the region;

[0016] (b) disposing the coded data within a region on the surface

[0017] Preferably, in the first and second aspect, the coded data takesthe form of at least one tag. In a preferred form, there a plurality ofthe tags substantially fill the region.

[0018] Preferably, each of the tags within a region are identical toeach other, but are distinct from tags in a plurality of other regions.

[0019] In a particularly preferred form, the tags are printed onto asurface in the form of a piece of paper, and are configured to be readby a sensing device in the form of an optical sensing stylus. The tagsare preferably printed using an ink that absorbs near infrared light butis substantially invisible to a human viewer under normal lightingconditions. When a user brings a sensing end of the stylus close to thesurface, one or more of the tags are imaged, interpreted and decoded toprovide an indication of the identity of the region from which the tagwas imaged. This information can be used in a number of useful ways,including controlling a computer via interactive elements.

[0020] Further aspects of the invention will become apparent fromreading the following detailed description of preferred and otherembodiments of the invention.

BRIEF DESCRIPTION OF DRAWINGS

[0021] Preferred and other embodiments of the invention will now bedescribed, by way of non-limiting example only, with reference to theaccompanying drawings, in which:

[0022]FIG. 1 is a schematic of a the relationship between a sampleprinted netpage and its online page description;

[0023]FIG. 2 is a schematic view of a interaction between a netpage pen,a netpage printer, a netpage page server, and a netpage applicationserver;

[0024]FIG. 3 illustrates a collection of netpage servers and printersinterconnected via a network;

[0025]FIG. 4 is a schematic view of a high-level structure of a printednetpage and its online page description;

[0026]FIG. 5 is a plan view showing a structure of a netpage tag;

[0027]FIG. 6 is a plan view showing a relationship between a set of thetags shown in FIG. 5 and a field of view of a netpage sensing device inthe form of a netpage pen;

[0028]FIG. 7 is a flowchart of a tag image processing and decodingalgorithm;

[0029]FIG. 8 is a perspective view of a netpage pen and its associatedtag-sensing field-of-view cone;

[0030]FIG. 9 is a perspective exploded view of the netpage pen shown inFIG. 8;

[0031]FIG. 10 is a schematic block diagram of a pen controller for thenetpage pen shown in FIGS. 8 and 9;

[0032]FIG. 11 is a perspective view of a wall-mounted netpage printer;

[0033]FIG. 12 is a section through the length of the netpage printer ofFIG. 11;

[0034]FIG. 12a is an enlarged portion of FIG. 12 showing a section ofthe duplexed print engines and glue wheel assembly;

[0035]FIG. 13 is a detailed view of the ink cartridge, ink, air and gluepaths, and print engines of the netpage printer of FIGS. 11 and 12;

[0036]FIG. 14 is a schematic block diagram of a printer controller forthe netpage printer shown in FIGS. 11 and 12;

[0037]FIG. 15 is a schematic block diagram of duplexed print enginecontrollers and Memjet™ printheads associated with the printercontroller shown in FIG. 14;

[0038]FIG. 16 is a schematic block diagram of the print enginecontroller shown in FIGS. 14 and 15;

[0039]FIG. 17 is a perspective view of a single Memjet™ printingelement, as used in, for example, the netpage printer of FIGS. 10 to 12;

[0040]FIG. 18 is a perspective view of a small part of an array ofMemjet™ printing elements;

[0041]FIG. 19 is a series of perspective views illustrating theoperating cycle of the Memjet™ printing element shown in FIG. 13;

[0042]FIG. 20 is a perspective view of a short segment of a pagewidthMemjet™ printhead;

[0043]FIG. 21 is a schematic view of a user class diagram;

[0044]FIG. 22 is a schematic view of a printer class diagram;

[0045]FIG. 23 is a schematic view of a pen class diagram;

[0046]FIG. 24 is a schematic view of an application class diagram;

[0047]FIG. 25 is a schematic view of a document and page descriptionclass diagram;

[0048]FIG. 26 is a schematic view of a document and page ownership classdiagram;

[0049]FIG. 27 is a schematic view of a terminal element specializationclass diagram;

[0050]FIG. 28 is a schematic view of a static element specializationclass diagram;

[0051]FIG. 29 is a schematic view of a hyperlink element class diagram;

[0052]FIG. 30 is a schematic view of a hyperlink element specializationclass diagram;

[0053]FIG. 31 is a schematic view of a hyperlinked group class diagram;

[0054]FIG. 32 is a schematic view of a form class diagram;

[0055]FIG. 33 is a schematic view of a digital ink class diagram;

[0056]FIG. 34 is a schematic view of a field element specializationclass diagram;

[0057]FIG. 35 is a schematic view of a checkbox field class diagram;

[0058]FIG. 36 is a schematic view of a text field class diagram;

[0059]FIG. 37 is a schematic view of a signature field class diagram;

[0060]FIG. 38 is a flowchart of an input processing algorithm;

[0061]FIG. 38a is a detailed flowchart of one step of the flowchart ofFIG. 38;

[0062]FIG. 39 is a schematic view of a page server command element classdiagram;

[0063]FIG. 40 is a schematic view of a resource description classdiagram;

[0064]FIG. 41 is a schematic view of a favorites list class diagram;

[0065]FIG. 42 is a schematic view of a history list class diagram;

[0066]FIG. 43 is a schematic view of a subscription delivery protocol;

[0067]FIG. 44 is a schematic view of a hyperlink request class diagram;

[0068]FIG. 45 is a schematic view of a hyperlink activation protocol;

[0069]FIG. 46 is a schematic view of a form submission protocol;

[0070]FIG. 47 is a schematic view of a commission payment protocol;

[0071]FIG. 48 is a schematic view of a set of radial wedges making up asymbol;

[0072]FIG. 49 is a schematic view of a ring A and B symbol allocationscheme;

[0073]FIG. 50 is a schematic view of a first ring C and D symbolallocation scheme;

[0074]FIG. 51 is a schematic view of a second ring C and D symbolallocation scheme;

[0075]FIG. 52 is a schematic view of a triangular tag packing;

[0076]FIG. 53 is a perspective view of an icosahedron;

[0077]FIG. 54 is a perspective view of an icosahedral geodesic withfrequency 3;

[0078]FIG. 55 is a schematic view of a minimum tag spacing;

[0079]FIG. 56 is a schematic view of a minimum tag spacing which avoidsoverlap;

[0080]FIG. 57 is a schematic view of a first tag insertion case;

[0081]FIG. 58 is a schematic view of a second tag insertion case;

[0082]FIG. 59 is a schematic view of a third tag insertion case;

[0083]FIG. 60 is a schematic view of a fourth tag insertion case;

[0084]FIG. 61 is a schematic view of a pen orientation relative to asurface;

[0085]FIG. 62 is a schematic view of a pen pitch geometry;

[0086]FIG. 63 is a schematic view of a pen roll geometry;

[0087]FIG. 64 is a schematic view of a pen coordinate space showingphysical and optical axes of a pen;

[0088]FIG. 65 is a schematic view of a curved nib geometry;

[0089]FIG. 66 is a schematic view of an interaction between samplingfrequency and tag frequency;

[0090]FIG. 67 is a table containing equations numbered 1 to 10;

[0091]FIG. 68 is a table containing equations numbered 11 to 20;

[0092]FIG. 69 is a table containing equations numbered 21 to 26;

[0093]FIG. 70 is a table containing equations numbered 27 to 34;

[0094]FIG. 71 is a table containing equations numbered 35 to 41;

[0095]FIG. 72 is a table containing equations numbered 42 to 44;

[0096]FIG. 73 is a table containing equations numbered 45 to 47;

[0097]FIG. 74 is a table containing equations numbered 48 to 51;

[0098]FIG. 75 is a table containing equations numbered 52 to 54;

[0099]FIG. 76 is a table containing equations numbered 55 to 57;

[0100]FIG. 77 is a table containing equations numbered 58 to 59;

[0101]FIG. 78 is a table containing equations numbered 60 to 63;

[0102]FIG. 79 is a table containing equations numbered 64 to 74;

[0103]FIG. 80 is a table containing equations numbered 75 to 86;

[0104]FIG. 81 is a table containing equations numbered 87 to 99;

[0105]FIG. 82 is a table containing equations numbered 100 to 111;

[0106]FIG. 83 is a table containing equations numbered 112 to 120;

[0107]FIG. 84 is a table containing equations numbered 121 to 129;

[0108]FIG. 85 is a table containing a set of degenerate forms ofequations 64 to 71;

[0109]FIG. 86 is a first part of a table containing conditions andspecial handling for zero pitch and zero roll; and

[0110]FIG. 87 is a the second part of the table of FIG. 86.

DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0111] Note: Memjet™ is a trade mark of Silverbrook Research Pty Ltd,Australia.

[0112] In the preferred embodiment, the invention is configured to workwith the netpage networked computer system, a detailed overview of whichfollows. It will be appreciated that not every implementation willnecessarily embody all or even most of the specific details andextensions discussed below in relation to the basic system. However, thesystem is described in its most complete form to reduce the need forexternal reference when attempting to understand the context in whichthe preferred embodiments and aspects of the present invention operate.

[0113] In brief summary, the preferred form of the netpage systememploys a computer interface in the form of a mapped surface, that is, aphysical surface which contains references to a map of the surfacemaintained in a computer system. The map references can be queried by anappropriate sensing device. Depending upon the specific implementation,the map references may be encoded visibly or invisibly, and defined insuch a way that a local query on the mapped surface yields anunambiguous map reference both within the map and among different maps.The computer system can contain information about features on the mappedsurface, and such information can be retrieved based on map referencessupplied by a sensing device used with the mapped surface. Theinformation thus retrieved can take the form of actions which areinitiated by the computer system on behalf of the operator in responseto the operator's interaction with the surface features.

[0114] In its preferred form, the netpage system relies on theproduction of, and human interaction with, netpages. These are pages oftext, graphics and images printed on ordinary paper, but which work likeinteractive web pages. Information is encoded on each page using inkwhich is substantially invisible to the unaided human eye. The ink,however, and thereby the coded data, can be sensed by an opticallyimaging pen and transmitted to the netpage system.

[0115] In the preferred form, active buttons and hyperlinks on each pagecan be clicked with the pen to request information from the network orto signal preferences to a network server. In one embodiment, textwritten by hand on a netpage is automatically recognized and convertedto computer text in the netpage system, allowing forms to be filled in.In other embodiments, signatures recorded on a netpage are automaticallyverified, allowing e-commerce transactions to be securely authorized.

[0116] As illustrated in FIG. 1, a printed netpage 1 can represent ainteractive form which can be filled in by the user both physically, onthe printed page, and “electronically”, via communication between thepen and the netpage system. The example shows a “Request” formcontaining name and address fields and a submit button. The netpageconsists of graphic data 2 printed using visible ink, and coded data 3printed as a collection of tags 4 using invisible ink. The correspondingpage description 5, stored on the netpage network, describes theindividual elements of the netpage. In particular it describes the typeand spatial extent (zone) of each interactive element (i.e. text fieldor button in the example), to allow the netpage system to correctlyinterpret input via the netpage. The submit button 6, for example, has azone 7 which corresponds to the spatial extent of the correspondinggraphic 8.

[0117] As illustrated in FIG. 2, the netpage pen 101, a preferred formof which is shown in FIGS. 8 and 9 and described in more detail below,works in conjunction with a netpage printer 601, an Internet-connectedprinting appliance for home, office or mobile use. The pen is wirelessand communicates securely with the netpage printer via a short-rangeradio link 9.

[0118] The netpage printer 601, a preferred form of which is shown inFIGS. 11 to 13 and described in more detail below, is able to deliver,periodically or on demand, personalized newspapers, magazines, catalogs,brochures and other publications, all printed at high quality asinteractive netpages. Unlike a personal computer, the netpage printer isan appliance which can be, for example, wall-mounted adjacent to an areawhere the morning news is first consumed, such as in a user's kitchen,near a breakfast table, or near the household's point of departure forthe day. It also comes in tabletop, desktop, portable and miniatureversions.

[0119] Netpages printed at their point of consumption combine theease-of-use of paper with the timeliness and interactivity of aninteractive medium.

[0120] As shown in FIG. 2, the netpage pen 101 interacts with the codeddata on a printed netpage 1 and communicates, via a short-range radiolink 9, the interaction to a netpage printer. The printer 601 sends theinteraction to the relevant netpage page server 10 for interpretation.In appropriate circumstances, the page server sends a correspondingmessage to application computer software running on a netpageapplication server 13. The application server may in turn send aresponse which is printed on the originating printer.

[0121] The netpage system is made considerably more convenient in thepreferred embodiment by being used in conjunction with high-speedmicroelectromechanical system (MEMS) based inkjet (Memjet™) printers. Inthe preferred form of this technology, relatively high-speed andhigh-quality printing is made more affordable to consumers. In itspreferred form, a netpage publication has the physical characteristicsof a traditional newsmagazine, such as a set of letter-size glossy pagesprinted in full color on both sides, bound together for easy navigationand comfortable handling.

[0122] The netpage printer exploits the growing availability ofbroadband Internet access. Cable service is available to 95% ofhouseholds in the United States, and cable modem service offeringbroadband Internet access is already available to 20% of these. Thenetpage printer can also operate with slower connections, but withlonger delivery times and lower image quality. Indeed, the netpagesystem can be enabled using existing consumer inkjet and laser printers,although the system will operate more slowly and will therefore be lessacceptable from a consumer's point of view. In other embodiments, thenetpage system is hosted on a private intranet. In still otherembodiments, the netpage system is hosted on a single computer orcomputer-enabled device, such as a printer.

[0123] Netpage publication servers 14 on the netpage network areconfigured to deliver print-quality publications to netpage printers.Periodical publications are delivered automatically to subscribingnetpage printers via pointcasting and multicasting Internet protocols.Personalized publications are filtered and formatted according toindividual user profiles.

[0124] A netpage printer can be configured to support any number ofpens, and a pen can work with any number of netpage printers. In thepreferred implementation, each netpage pen has a unique identifier. Ahousehold may have a collection of colored netpage pens, one assigned toeach member of the family. This allows each user to maintain a distinctprofile with respect to a netpage publication server or applicationserver.

[0125] A netpage pen can also be registered with a netpage registrationserver 11 and linked to one or more payment card accounts. This allowse-commerce payments to be securely authorized using the netpage pen. Thenetpage registration server compares the signature captured by thenetpage pen with a previously registered signature, allowing it toauthenticate the user's identity to an e-commerce server. Otherbiometrics can also be used to verify identity. A version of the netpagepen includes fingerprint scanning, verified in a similar way by thenetpage registration server.

[0126] Although a netpage printer may deliver periodicals such as themorning newspaper without user intervention, it can be configured neverto deliver unsolicited junk mail. In its preferred form, it onlydelivers periodicals from subscribed or otherwise authorized sources. Inthis respect, the netpage printer is unlike a fax machine or e-mailaccount which is visible to any junk mailer who knows the telephonenumber or email address.

[0127] 1 Netpage System Architecture

[0128] Each object model in the system is described using a UnifiedModeling Language (UML) class diagram. A class diagram consists of a setof object classes connected by relationships, and two kinds ofrelationships are of interest here: associations and generalizations. Anassociation represents some kind of relationship between objects, i.e.between instances of classes. A generalization relates actual classes,and can be understood in the following way: if a class is thought of asthe set of all objects of that class, and class A is a generalization ofclass B, then B is simply a subset of A. The UML does not directlysupport second-order modelling—i.e. classes of classes.

[0129] Each class is drawn as a rectangle labelled with the name of theclass. It contains a list of the attributes of the class, separated fromthe name by a horizontal line, and a list of the operations of theclass, separated from the attribute list by a horizontal line. In theclass diagrams which follow, however, operations are never modelled.

[0130] An association is drawn as a line joining two classes, optionallylabelled at either end with the multiplicity of the association. Thedefault multiplicity is one. An asterisk (*) indicates a multiplicity of“many”, i.e. zero or more. Each association is optionally labelled withits name, and is also optionally labelled at either end with the role ofthe corresponding class. An open diamond indicates an aggregationassociation (“is-part-of”), and is drawn at the aggregator end of theassociation line.

[0131] A generalization relationship (“is-a”) is drawn as a solid linejoining two classes, with an arrow (in the form of an open triangle) atthe generalization end.

[0132] When a class diagram is broken up into multiple diagrams, anyclass which is duplicated is shown with a dashed outline in all but themain diagram which defines it. It is shown with attributes only where itis defined.

[0133] 1.1 Netpages

[0134] Netpages are the foundation on which a netpage network is built.They provide a paper-based user interface to published information andinteractive services.

[0135] A netpage consists of a printed page (or other surface region)invisibly tagged with references to an online description of the page.The online page description is maintained persistently by a netpage pageserver. The page description describes the visible layout and content ofthe page, including text, graphics and images. It also describes theinput elements on the page, including buttons, hyperlinks, and inputfields. A netpage allows markings made with a netpage pen on its surfaceto be simultaneously captured and processed by the netpage system.

[0136] Multiple netpages can share the same page description. However,to allow input through otherwise identical pages to be distinguished,each netpage is assigned a unique page identifier. This page ID hassufficient precision to distinguish between a very large number ofnetpages.

[0137] Each reference to the page description is encoded in a printedtag. The tag identifies the unique page on which it appears, and therebyindirectly identifies the page description. The tag also identifies itsown position on the page. Characteristics of the tags are described inmore detail below.

[0138] Tags are printed in infrared-absorptive ink on any substratewhich is infrared-reflective, such as ordinary paper. Near-infraredwavelengths are invisible to the human eye but are easily sensed by asolid-state image sensor with an appropriate filter.

[0139] A tag is sensed by an area image sensor in the netpage pen, andthe tag data is transmitted to the netpage system via the nearestnetpage printer. The pen is wireless and communicates with the netpageprinter via a short-range radio link. Tags are sufficiently small anddensely arranged that the pen can reliably image at least one tag evenon a single click on the page. It is important that the pen recognizethe page ID and position on every interaction with the page, since theinteraction is stateless. Tags are error-correctably encoded to makethem partially tolerant to surface damage.

[0140] The netpage page server maintains a unique page instance for eachprinted netpage, allowing it to maintain a distinct set of user-suppliedvalues for input fields in the page description for each printednetpage.

[0141] The relationship between the page description, the page instance,and the printed netpage is shown in FIG. 4. The page instance isassociated with both the netpage printer which printed it and, if known,the netpage user who requested it.

[0142] 1.2 Netpage Tags

[0143] 1.2.1 Tag Data Content

[0144] In a preferred form, each tag identifies the region in which itappears, and the location of that tag within the region. A tag may alsocontain flags which relate to the region as a whole or to the tag. Oneor more flag bits may, for example, signal a tag sensing device toprovide feedback indicative of a function associated with the immediatearea of the tag, without the sensing device having to refer to adescription of the region. A netpage pen may, for example, illuminate an“active area” LED when in the zone of a hyperlink.

[0145] As will be more clearly explained below, in a preferredembodiment, each tag contains an easily recognized invariant structurewhich aids initial detection, and which assists in minimizing the effectof any warp induced by the surface or by the sensing process. The tagspreferably tile the entire page, and are sufficiently small and denselyarranged that the pen can reliably image at least one tag even on asingle click on the page. It is important that the pen recognize thepage ID and position on every interaction with the page, since theinteraction is stateless.

[0146] In a preferred embodiment, the region to which a tag referscoincides with an entire page, and the region ID encoded in the tag istherefore synonymous with the page ID of the page on which the tagappears. In other embodiments, the region to which a tag refers can bean arbitrary subregion of a page or other surface. For example, it cancoincide with the zone of an interactive element, in which case theregion ID can directly identify the interactive element. TABLE 1 Tagdata Field Precision (bits) Region ID 100 Tag ID 16 Flags 4 Total 120

[0147] Each tag contains 120 bits of information, typically allocated asshown in Table 1. Assuming a maximum tag density of 64 per square inch,a 16-bit tag ID supports a region size of up to 1024 square inches.Larger regions can be mapped continuously without increasing the tag IDprecision simply by using abutting regions and maps. The 100-bit regionID allows 2¹⁰⁰ (˜10³⁰ or a million trillion trillion) different regionsto be uniquely identified.

[0148] 1.2.2 Tag Data Encoding

[0149] The 120 bits of tag data are redundantly encoded using a (15, 5)Reed-Solomon code. This yields 360 encoded bits consisting of 6codewords of 15 4-bit symbols each. The (15, 5) code allows up to 5symbol errors to be corrected per codeword, i.e. it is tolerant of asymbol error rate of up to 33% per codeword.

[0150] Each 4-bit symbol is represented in a spatially coherent way inthe tag, and the symbols of the six codewords are interleaved spatiallywithin the tag. This ensures that a burst error (an error affectingmultiple spatially adjacent bits) damages a minimum number of symbolsoverall and a minimum number of symbols in any one codeword, thusmaximising the likelihood that the burst error can be fully corrected.

[0151] 1.2.3 Physical Tag Structure

[0152] The physical representation of the tag, shown in FIG. 5, includesfixed target structures 15, 16, 17 and variable data areas 18. The fixedtarget structures allow a sensing device such as the netpage pen todetect the tag and infer its three-dimensional orientation relative tothe sensor. The data areas contain representations of the individualbits of the encoded tag data.

[0153] To achieve proper tag reproduction, the tag is rendered at aresolution of 256×256 dots. When printed at 1600 dots per inch thisyields a tag with a diameter of about 4 mm. At this resolution the tagis designed to be surrounded by a “quiet area” of radius 16 dots. Sincethe quiet area is also contributed by adjacent tags, it only adds 16dots to the effective diameter of the tag.

[0154] The tag includes six target structures: a detection ring 15; anorientation axis target 16; and four perspective targets 17.

[0155] The detection ring 15 allows the sensing device to initiallydetect the tag 4. The ring is easy to detect because it is rotationallyinvariant and because a simple correction of its aspect ratio removesmost of the effects of perspective distortion. The orientation axis 16allows the sensing device to determine the approximate planarorientation of the tag due to the yaw of the sensor. The orientationaxis is skewed to yield a unique orientation. The four perspectivetargets 17 allow the sensing device to infer an accurate two-dimensionalperspective transform of the tag and hence an accurate three-dimensionalposition and orientation of the tag relative to the sensor.

[0156] All target structures are redundantly large to improve theirimmunity to noise.

[0157] The overall tag shape is circular. This supports, amongst otherthings, optimal tag packing on an irregular triangular grid. Incombination with the circular detection ring 15, this makes a circulararrangement of data bits within the tag optimal. To maximise its size,each data bit is represented by a radial wedge 510 in the form of anarea bounded by two radial lines 512, a radially inner arc 514 and aradially outer arc 516. Each wedge 510 has a minimum dimension of 8 dotsat 1600 dpi and is designed so that its base (i.e. its inner arc 514),is at least equal to this minimum dimension. The radial height of thewedge 510 is always equal to the minimum dimension. Each 4-bit datasymbol is represented by an array 518 of 2×2 wedges 510, as best shownin FIG. 48.

[0158] The 15 4-bit data symbols of each of the six codewords areallocated to the four concentric symbol rings 18 a to 18 d, shown inFIG. 5, in interleaved fashion as shown in FIGS. 49 to 51. Symbols offirst to sixth codewords 520-525 are allocated alternately in circularprogression around the tag.

[0159] The interleaving is designed to maximise the average spatialdistance between any two symbols of the same codeword.

[0160] In order to support “single-click” interaction with a taggedregion via a sensing device, the sensing device must be able to see atleast one entire tag in its field of view no matter where in the regionor at what orientation it is positioned. The required diameter of thefield of view of the sensing device is therefore a function of the sizeand spacing of the tags.

[0161] Assuming a circular tag shape, the minimum diameter of the sensorfield of view is obtained when the tags are tiled on a equilateraltriangular grid, as shown in FIG. 6.

[0162] 1.2.4 Tag Image Processing and Decoding

[0163] The tag image processing and decoding performed by a sensingdevice such as the netpage pen is shown in FIG. 7. While a capturedimage is being acquired from the image sensor, the dynamic range of theimage is determined (at 20). The center of the range is then chosen asthe binary threshold for the image 21. The image is then thresholded andsegmented into connected pixel regions (i.e. shapes 23) (at 22). Shapeswhich are too small to represent tag target structures are discarded.The size and centroid of each shape is also computed.

[0164] Binary shape moments 25 are then computed (at 24) for each shape,and these provide the basis for subsequently locating target structures.Central shape moments are by their nature invariant of position, and canbe easily made invariant of scale, aspect ratio and rotation.

[0165] The ring target structure 15 is the first to be located (at 26).A ring has the advantage of being very well behaved whenperspective-distorted. Matching proceeds by aspect-normalizing androtation-normalizing each shape's moments. Once its second-order momentsare normalized the ring is easy to recognize even if the perspectivedistortion was significant. The ring's original aspect and rotation 27together provide a useful approximation of the perspective transform.

[0166] The axis target structure 16 is the next to be located (at 28).Matching proceeds by applying the ring's normalizations to each shape'smoments, and rotation-normalizing the resulting moments. Once itssecond-order moments are normalized the axis target is easilyrecognized. Note that one third order moment is required to disambiguatethe two possible orientations of the axis. The shape is deliberatelyskewed to one side to make this possible. Note also that it is onlypossible to rotation-normalize the axis target after it has had thering's normalizations applied, since the perspective distortion can hidethe axis target's axis. The axis target's original rotation provides auseful approximation of the tag's rotation due to pen yaw 29.

[0167] The four perspective target structures 17 are the last to belocated (at 30). Good estimates of their positions are computed based ontheir known spatial relationships to the ring and axis targets, theaspect and rotation of the ring, and the rotation of the axis. Matchingproceeds by applying the ring's normalizations to each shape's moments.Once their second-order moments are normalized the circular perspectivetargets are easy to recognize, and the target closest to each estimatedposition is taken as a match. The original centroids of the fourperspective targets are then taken to be the perspective-distortedcorners 31 of a square of known size in tag space, and aneight-degree-of-freedom perspective transform 33 is inferred (at 32)based on solving the well-understood equations relating the fourtag-space and image-space point pairs.

[0168] The inferred tag-space to image-space perspective transform isused to project (at 36) each known data bit position in tag space intoimage space where the real-valued position is used to bilinearlyinterpolate (at 36) the four relevant adjacent pixels in the inputimage. The previously computed image threshold 21 is used to thresholdthe result to produce the final bit value 37.

[0169] Once all 360 data bits 37 have been obtained in this way, each ofthe six 60-bit Reed-Solomon codewords is decoded (at 38) to yield 20decoded bits 39, or 120 decoded bits in total. Note that the codewordsymbols are sampled in codeword order, so that codewords are implicitlyde-interleaved during the sampling process.

[0170] The ring target 15 is only sought in a subarea of the image whoserelationship to the image guarantees that the ring, if found, is part ofa complete tag. If a complete tag is not found and successfully decoded,then no pen position is recorded for the current frame. Given adequateprocessing power and ideally a non-minimal field of view 193, analternative strategy involves seeking another tag in the current image.

[0171] The obtained tag data indicates the identity of the regioncontaining the tag and the position of the tag within the region. Anaccurate position 35 of the pen nib in the region, as well as theoverall orientation 35 of the pen, is then inferred (at 34) from theperspective transform 33 observed on the tag and the known spatialrelationship between the pen's physical axis and the pen's optical axis.

[0172] 1.2.5 Tag Map

[0173] Decoding a tag results in a region ID, a tag ID, and atag-relative pen transform. Before the tag ID and the tag-relative penlocation can be translated into an absolute location within the taggedregion, the location of the tag within the region must be known. This isgiven by a tag map, a function which maps each tag ID in a tagged regionto a corresponding location. The tag map class diagram is shown in FIG.22, as part of the netpage printer class diagram.

[0174] A tag map reflects the scheme used to tile the surface regionwith tags, and this can vary according to surface type. When multipletagged regions share the same tiling scheme and the same tag numberingscheme, they can also share the same tag map.

[0175] The tag map for a region must be retrievable via the region ID.Thus, given a region ID, a tag ID and a pen transform, the tag map canbe retrieved, the tag ID can be translated into an absolute tag locationwithin the region, and the tag-relative pen location can be added to thetag location to yield an absolute pen location within the region.

[0176] 1.2.6 Tagging Schemes

[0177] Two distinct surface coding schemes are of interest, both ofwhich use the tag structure described earlier in this section. Thepreferred coding scheme uses “location-indicating” tags as alreadydiscussed. An alternative coding scheme uses object-indicating tags.

[0178] A location-indicating tag contains a tag ID which, whentranslated through the tag map associated with the tagged region, yieldsa unique tag location within the region. The tag-relative location ofthe pen is added to this tag location to yield the location of the penwithin the region. This in turn is used to determine the location of thepen relative to a user interface element in the page descriptionassociated with the region. Not only is the user interface elementitself identified, but a location relative to the user interface elementis identified. Location-indicating tags therefore trivially support thecapture of an absolute pen path in the zone of a particular userinterface element.

[0179] An object-indicating tag contains a tag ID which directlyidentifies a user interface element in the page description associatedwith the region. All the tags in the zone of the user interface elementidentify the user interface element, making them all identical andtherefore indistinguishable. Object-indicating tags do not, therefore,support the capture of an absolute pen path. They do, however, supportthe capture of a relative pen path. So long as the position samplingfrequency exceeds twice the encountered tag frequency, the displacementfrom one sampled pen position to the next within a stroke can beunambiguously determined.

[0180] Assume a sampling wavelength of λ_(S) and a tag wavelength ofλ_(T), with a relationship as defined in EQ 38. For two adjacentposition samples P_(i) and P_(i+1), one of EQ 39 and EQ 40 will hold.

[0181] Assuming both equations hold leads to the relationship defined inEQ 41.

[0182] Since EQ 41 contradicts EQ 38, the assumption that both EQ 39 andEQ 40 hold must be incorrect, and the choice is therefore unambiguous,as stated.

[0183] The illustration in FIG. 60 shows four tags 500 and aone-dimensional stroke of six sample positions 582 which satisfy EQ 38.Possible aliases 584 of the sample positions are also shown. Frominspection, if the distance from one sample position to the next isλ_(S), then the distance from a sample position to the alias of the nextsample position exceeds λ_(S).

[0184] If the tag wavelength λ_(T) is 4.7 mm, as discussed in earlier,then the sampling wavelength λ_(S) must be less than 2.35 mm. If thetemporal sampling frequency is 100 Hz as required for accuratehandwriting recognition, then the pen speed must be less than 235 mm/sto satisfy EQ 38.

[0185] With either tagging scheme, the tags function in cooperation withassociated visual elements on the netpage as user interactive elementsin that a user can interact with the printed page using an appropriatesensing device in order for tag data to be read by the sensing deviceand for an appropriate response to be generated in the netpage system.

[0186] 1.3 Document and Page Descriptions

[0187] A preferred embodiment of a document and page description classdiagram is shown in FIGS. 25 and 26.

[0188] In the netpage system a document is described at three levels. Atthe most abstract level the document 836 has a hierarchical structurewhose terminal elements 839 are associated with content objects 840 suchas text objects, text style objects, image objects, etc. Once thedocument is printed on a printer with a particular page size andaccording to a particular user's scale factor preference, the documentis paginated and otherwise formatted. Formatted terminal elements 835will in some cases be associated with content objects which aredifferent from those associated with their corresponding terminalelements, particularly where the content objects are style-related. Eachprinted instance of a document and page is also described separately, toallow input captured through a particular page instance 830 to berecorded separately from input captured through other instances of thesame page description.

[0189] The presence of the most abstract document description on thepage server allows a user to request a copy of a document without beingforced to accept the source document's specific format. The user may berequesting a copy through a printer with a different page size, forexample. Conversely, the presence of the formatted document descriptionon the page server allows the page server to efficiently interpret useractions on a particular printed page.

[0190] A formatted document 834 consists of a set of formatted pagedescriptions 5, each of which consists of a set of formatted terminalelements 835. Each formatted element has a spatial extent or zone 58 onthe page. This defines the active area of input elements such ashyperlinks and input fields.

[0191] A document instance 831 corresponds to a formatted document 834.It consists of a set of page instances 830, each of which corresponds toa page description 5 of the formatted document. Each page instance 830describes a single unique printed netpage 1, and records the page ID 50of the netpage. A page instance is not part of a document instance if itrepresents a copy of a page requested in isolation.

[0192] A page instance consists of a set of terminal element instances832. An element instance only exists if it records instance-specificinformation. Thus, a hyperlink instance exists for a hyperlink elementbecause it records a transaction ID 55 which is specific to the pageinstance, and a field instance exists for a field element because itrecords input specific to the page instance. An element instance doesnot exist, however, for static elements such as textflows.

[0193] A terminal element can be a static element 843, a hyperlinkelement 844, a field element 845 or a page server command element 846,as shown in FIG. 27. A static element 843 can be a style element 847with an associated style object 854, a textflow element 848 with anassociated styled text object 855, an image element 849 with anassociated image element 856, a graphic element 850 with an associatedgraphic object 857, a video clip element 851 with an associated videoclip object 858, an audio clip element 852 with an associated audio clipobject 859, or a script element 853 with an associated script object860, as shown in FIG. 28.

[0194] A page instance has a background field 833 which is used torecord any digital ink captured on the page which does not apply to aspecific input element.

[0195] In the preferred form of the invention, a tag map 811 isassociated with each page instance to allow tags on the page to betranslated into locations on the page.

[0196] 1.4 The Netpage Network

[0197] In a preferred embodiment, a netpage network consists of adistributed set of netpage page servers 10, netpage registration servers11, netpage ID servers 12, netpage application servers 13, netpagepublication servers 14, and netpage printers 601 connected via a network19 such as the Internet, as shown in FIG. 3.

[0198] The netpage registration server 11 is a server which recordsrelationships between users, pens, printers, applications andpublications, and thereby authorizes various network activities. Itauthenticates users and acts as a signing proxy on behalf ofauthenticated users in application transactions. It also provideshandwriting recognition services. As described above, a netpage pageserver 10 maintains persistent information about page descriptions andpage instances. The netpage network includes any number of page servers,each handling a subset of page instances. Since a page server alsomaintains user input values for each page instance, clients such asnetpage printers send netpage input directly to the appropriate pageserver. The page server interprets any such input relative to thedescription of the corresponding page.

[0199] A netpage ID server 12 allocates document IDs 51 on demand, andprovides load-balancing of page servers via its ID allocation scheme.

[0200] A netpage printer uses the Internet Distributed Name System(DNS), or similar, to resolve a netpage page ID 50 into the networkaddress of the netpage page server handling the corresponding pageinstance.

[0201] A netpage application server 13 is a server which hostsinteractive netpage applications. A netpage publication server 14 is anapplication server which publishes netpage documents to netpageprinters. They are described in detail in Section 2.

[0202] Netpage servers can be hosted on a variety of network serverplatforms from manufacturers such as IBM, Hewlett-Packard, and Sun.Multiple netpage servers can run concurrently on a single host, and asingle server can be distributed over a number of hosts. Some or all ofthe functionality provided by netpage servers, and in particular thefunctionality provided by the ID server and the page server, can also beprovided directly in a netpage appliance such as a netpage printer, in acomputer workstation, or on a local network.

[0203] 1.5 The Netpage Printer

[0204] The netpage printer 601 is an appliance which is registered withthe netpage system and prints netpage documents on demand and viasubscription. Each printer has a unique printer ID 62, and is connectedto the netpage network via a network such as the Internet, ideally via abroadband connection.

[0205] Apart from identity and security settings in non-volatile memory,the netpage printer contains no persistent storage. As far as a user isconcerned, “the network is the computer”. Netpages functioninteractively across space and time with the help of the distributednetpage page servers 10, independently of particular netpage printers.

[0206] The netpage printer receives subscribed netpage documents fromnetpage publication servers 14. Each document is distributed in twoparts: the page layouts, and the actual text and image objects whichpopulate the pages. Because of personalization, page layouts aretypically specific to a particular subscriber and so are pointcast tothe subscriber's printer via the appropriate page server. Text and imageobjects, on the other hand, are typically shared with other subscribers,and so are multicast to all subscribers' printers and the appropriatepage servers.

[0207] The netpage publication server optimizes the segmentation ofdocument content into pointcasts and multicasts. After receiving thepointcast of a document's page layouts, the printer knows whichmulticasts, if any, to listen to.

[0208] Once the printer has received the complete page layouts andobjects that define the document to be printed, it can print thedocument.

[0209] The printer rasterizes and prints odd and even pagessimultaneously on both sides of the sheet. It contains duplexed printengine controllers 760 and print engines utilizing Memjet™ printheads350 for this purpose.

[0210] The printing process consists of two decoupled stages:rasterization of page descriptions, and expansion and printing of pageimages. The raster image processor (RIP) consists of one or morestandard DSPs 757 running in parallel. The duplexed print enginecontrollers consist of custom processors which expand, dither and printpage images in real time, synchronized with the operation of theprintheads in the print engines.

[0211] Printers not enabled for IR printing have the option to printtags using IR-absorptive black ink, although this restricts tags tootherwise empty areas of the page. Although such pages have more limitedfunctionality than IR-printed pages, they are still classed as netpages.

[0212] A normal netpage printer prints netpages on sheets of paper. Morespecialised netpage printers may print onto more specialised surfaces,such as globes. Each printer supports at least one surface type, andsupports at least one tag tiling scheme, and hence tag map, for eachsurface type. The tag map 811 which describes the tag tiling schemeactually used to print a document becomes associated with that documentso that the document's tags can be correctly interpreted.

[0213]FIG. 2 shows the netpage printer class diagram, reflectingprinter-related information maintained by a registration server 11 onthe netpage network.

[0214] A preferred embodiment of the netpage printer is described ingreater detail in Section 6 below, with reference to FIGS. 11 to 16.

[0215] 1.5.1 Memjet™ Printheads

[0216] The netpage system can operate using printers made with a widerange of digital printing technologies, including thermal inkjet,piezoelectric inkjet, laser electrophotographic, and others. However,for wide consumer acceptance, it is desirable that a netpage printerhave the following characteristics:

[0217] photographic quality color printing

[0218] high quality text printing

[0219] high reliability

[0220] low printer cost

[0221] low ink cost

[0222] low paper cost

[0223] simple operation

[0224] nearly silent printing

[0225] high printing speed

[0226] simultaneous double sided printing

[0227] compact form factor

[0228] low power consumption

[0229] No commercially available printing technology has all of thesecharacteristics

[0230] To enable to production of printers with these characteristics,the present applicant has invented a new print technology, referred toas Memjet™ technology. Memjet™ is a drop-on-demand inkjet technologythat incorporates pagewidth printheads fabricated usingmicroelectromechanical systems (MEMS) technology. FIG. 17 shows a singleprinting element 300 of a Memjet™ printhead. The netpage wallprinterincorporates 168960 printing elements 300 to form a 1600 dpi pagewidthduplex printer. This printer simultaneously prints cyan, magenta,yellow, black, and infrared inks as well as paper conditioner and inkfixative.

[0231] The printing element 300 is approximately 110 microns long by 32microns wide. Arrays of these printing elements are formed on a siliconsubstrate 301 that incorporates CMOS logic, data transfer, timing, anddrive circuits (not shown).

[0232] Major elements of the printing element 300 are the nozzle 302,the nozzle rim 303, the nozzle chamber 304, the fluidic seal 305, theink channel rim 306, the lever arm 307, the active actuator beam pair308, the passive actuator beam pair 309, the active actuator anchor 310,the passive actuator anchor 311, and the ink inlet 312.

[0233] The active actuator beam pair 308 is mechanically joined to thepassive actuator beam pair 309 at the join 319. Both beams pairs areanchored at their respective anchor points 310 and 311. The combinationof elements 308, 309, 310, 311, and 319 form a cantileveredelectrothermal bend actuator 320.

[0234]FIG. 18 shows a small part of an array of printing elements 300,including a cross section 315 of a printing element 300. The crosssection 315 is shown without ink, to clearly show the ink inlet 312 thatpasses through the silicon wafer 301.

[0235] FIGS. 19(a), 19(b) and 19(c) show the operating cycle of aMemjet™ printing element 300.

[0236]FIG. 19(a) shows the quiescent position of the ink meniscus 316prior to printing an ink droplet. Ink is retained in the nozzle chamberby surface tension at the ink meniscus 316 and at the fluidic seal 305formed between the nozzle chamber 304 and the ink channel rim 306.

[0237] While printing, the printhead CMOS circuitry distributes datafrom the print engine controller to the correct printing element,latches the data, and buffers the data to drive the electrodes 318 ofthe active actuator beam pair 308. This causes an electrical current topass through the beam pair 308 for about one microsecond, resulting inJoule heating. The temperature increase resulting from Joule heatingcauses the beam pair 308 to expand. As the passive actuator beam pair309 is not heated, it does not expand, resulting in a stress differencebetween the two beam pairs. This stress difference is partially resolvedby the cantilevered end of the electrothermal bend actuator 320 bendingtowards the substrate 301. The lever arm 307 transmits this movement tothe nozzle chamber 304. The nozzle chamber 304 moves about two micronsto the position shown in FIG. 19(b). This increases the ink pressure,forcing ink 321 out of the nozzle 302, and causing the ink meniscus 316to bulge. The nozzle rim 303 prevents the ink meniscus 316 fromspreading across the surface of the nozzle chamber 304 As thetemperature of the beam pairs 308 and 309 equalizes, the actuator 320returns to its original position. This aids in the break-off of the inkdroplet 317 from the ink 321 in the nozzle chamber, as shown in FIG.19(c). The nozzle chamber is refilled by the action of the surfacetension at the meniscus 316.

[0238]FIG. 20 shows a segment of a printhead 350. In a netpage printer,the length of the printhead is the full width of the paper (typically210 mm) in the direction 351. The segment shown is 0.4 mm long (about0.2% of a complete printhead). When printing, the paper is moved pastthe fixed printhead in the direction 352. The printhead has 6 rows ofinterdigitated printing elements 300, printing the six colors or typesof ink supplied by the ink inlets 312.

[0239] To protect the fragile surface of the printhead during operation,a nozzle guard wafer 330 is attached to the printhead substrate 301. Foreach nozzle 302 there is a corresponding nozzle guard hole 331 throughwhich the ink droplets are fired. To prevent the nozzle guard holes 331from becoming blocked by paper fibers or other debris, filtered air ispumped through the air inlets 332 and out of the nozzle guard holesduring printing. To prevent ink 321 from drying, the nozzle guard issealed while the printer is idle.

[0240] 1.6 The Netpage Pen

[0241] The active sensing device of the netpage system is typically apen 101, which, using its embedded controller 134, is able to captureand decode IR position tags from a page via an image sensor. The imagesensor is a solid-state device provided with an appropriate filter topermit sensing at only near-infrared wavelengths. As described in moredetail below, the system is able to sense when the nib is in contactwith the surface, and the pen is able to sense tags at a sufficient rateto capture human handwriting (i.e. at 200 dpi or greater and 100 Hz orfaster). Information captured by the pen is encrypted and wirelesslytransmitted to the printer (or base station), the printer or basestation interpreting the data with respect to the (known) pagestructure.

[0242] The preferred embodiment of the netpage pen operates both as anormal marking ink pen and as a non-marking stylus. The marking aspect,however, is not necessary for using the netpage system as a browsingsystem, such as when it is used as an Internet interface. Each netpagepen is registered with the netpage system and has a unique pen ID 61.FIG. 23 shows the netpage pen class diagram, reflecting pen-relatedinformation maintained by a registration server 11 on the netpagenetwork.

[0243] When either nib is in contact with a netpage, the pen determinesits position and orientation relative to the page. The nib is attachedto a force sensor, and the force on the nib is interpreted relative to athreshold to indicate whether the pen is “up” or “down”. This allows ainteractive element on the page to be ‘clicked’ by pressing with the pennib, in order to request, say, information from a network. Furthermore,the force is captured as a continuous value to allow, say, the fulldynamics of a signature to be verified.

[0244] The pen determines the position and orientation of its nib on thenetpage by imaging, in the infrared spectrum, an area 193 of the page inthe vicinity of the nib. It decodes the nearest tag and computes theposition of the nib relative to the tag from the observed perspectivedistortion on the imaged tag and the known geometry of the pen optics.Although the position resolution of the tag may be low, because the tagdensity on the page is inversely proportional to the tag size, theadjusted position resolution is quite high, exceeding the minimumresolution required for accurate handwriting recognition.

[0245] Pen actions relative to a netpage are captured as a series ofstrokes. A stroke consists of a sequence of time-stamped pen positionson the page, initiated by a pen-down event and completed by thesubsequent pen-up event. A stroke is also tagged with the page ID 50 ofthe netpage whenever the page ID changes, which, under normalcircumstances, is at the commencement of the stroke.

[0246] Each netpage pen has a current selection 826 associated with it,allowing the user to perform copy and paste operations etc. Theselection is timestamped to allow the system to discard it after adefined time period. The current selection describes a region of a pageinstance. It consists of the most recent digital ink stroke capturedthrough the pen relative to the background area of the page. It isinterpreted in an application-specific manner once it is submitted to anapplication via a selection hyperlink activation.

[0247] Each pen has a current nib 824. This is the nib last notified bythe pen to the system. In the case of the default netpage pen describedabove, either the marking black ink nib or the non-marking stylus nib iscurrent. Each pen also has a current nib style 825. This is the nibstyle last associated with the pen by an application, e.g. in responseto the user selecting a color from a palette. The default nib style isthe nib style associated with the current nib. Strokes captured througha pen are tagged with the current nib style. When the strokes aresubsequently reproduced, they are reproduced in the nib style with whichthey are tagged.

[0248] Whenever the pen is within range of a printer with which it cancommunicate, the pen slowly flashes its “online” LED. When the pen failsto decode a stroke relative to the page, it momentarily activates its“error” LED. When the pen succeeds in decoding a stroke relative to thepage, it momentarily activates its “ok” LED.

[0249] A sequence of captured strokes is referred to as digital ink.Digital ink forms the basis for the digital exchange of drawings andhandwriting, for online recognition of handwriting, and for onlineverification of signatures.

[0250] The pen is wireless and transmits digital ink to the netpageprinter via a short-range radio link. The transmitted digital ink isencrypted for privacy and security and packetized for efficienttransmission, but is always flushed on a pen-up event to ensure timelyhandling in the printer.

[0251] When the pen is out-of-range of a printer it buffers digital inkin internal memory, which has a capacity of over ten minutes ofcontinuous handwriting. When the pen is once again within range of aprinter, it transfers any buffered digital ink.

[0252] A pen can be registered with any number of printers, but becauseall state data resides in netpages both on paper and on the network, itis largely immaterial which printer a pen is communicating with at anyparticular time.

[0253] A preferred embodiment of the pen is described in greater detailin Section 6 below, with reference to FIGS. 8 to 10.

[0254] 1.7 Netpage Interaction

[0255] The netpage printer 601 receives data relating to a stroke fromthe pen 101 when the pen is used to interact with a netpage 1. The codeddata 3 of the tags 4 is read by the pen when it is used to execute amovement, such as a stroke. The data allows the identity of theparticular page and associated interactive element to be determined andan indication of the relative positioning of the pen relative to thepage to be obtained. The indicating data is transmitted to the printer,where it resolves, via the DNS, the page ID 50 of the stroke into thenetwork address of the netpage page server 10 which maintains thecorresponding page instance 830. It then transmits the stroke to thepage server. If the page was recently identified in an earlier stroke,then the printer may already have the address of the relevant pageserver in its cache. Each netpage consists of a compact page layoutmaintained persistently by a netpage page server (see below). The pagelayout refers to objects such as images, fonts and pieces of text,typically stored elsewhere on the netpage network.

[0256] When the page server receives the stroke from the pen, itretrieves the page description to which the stroke applies, anddetermines which element of the page description the stroke intersects.It is then able to interpret the stroke in the context of the type ofthe relevant element.

[0257] A “click” is a stroke where the distance and time between the pendown position and the subsequent pen up position are both less than somesmall maximum. An object which is activated by a click typicallyrequires a click to be activated, and accordingly, a longer stroke isignored. The failure of a pen action, such as a “sloppy” click, toregister is indicated by the lack of response from the pen's “ok” LED.

[0258] There are two kinds of input elements in a netpage pagedescription: hyperlinks and form fields. Input through a form field canalso trigger the activation of an associated hyperlink.

[0259] 1.7.1 Hyperlinks

[0260] A hyperlink is a means of sending a message to a remoteapplication, and typically elicits a printed response in the netpagesystem.

[0261] A hyperlink element 844 identifies the application 71 whichhandles activation of the hyperlink, a link ID 54 which identifies thehyperlink to the application, an “alias required” flag which asks thesystem to include the user's application alias ID 65 in the hyperlinkactivation, and a description which is used when the hyperlink isrecorded as a favorite or appears in the user's history. The hyperlinkelement class diagram is shown in FIG. 29.

[0262] When a hyperlink is activated, the page server sends a request toan application somewhere on the network. The application is identifiedby an application ID 64, and the application ID is resolved in thenormal way via the DNS. There are three types of hyperlinks: generalhyperlinks 863, form hyperlinks 865, and selection hyperlinks 864, asshown in FIG. 30. A general hyperlink can implement a request for alinked document, or may simply signal a preference to a server. A formhyperlink submits the corresponding form to the application. A selectionhyperlink submits the current selection to the application. If thecurrent selection contains a single-word piece of text, for example, theapplication may return a single-page document giving the word's meaningwithin the context in which it appears, or a translation into adifferent language. Each hyperlink type is characterized by whatinformation is submitted to the application.

[0263] The corresponding hyperlink instance 862 records a transaction ID55 which can be specific to the page instance on which the hyperlinkinstance appears. The transaction ID can identify user-specific data tothe application, for example a “shopping cart” of pending purchasesmaintained by a purchasing application on behalf of the user.

[0264] The system includes the pen's current selection 826 in aselection hyperlink activation. The system includes the content of theassociated form instance 868 in a form hyperlink activation, although ifthe hyperlink has its “submit delta” attribute set, only input since thelast form submission is included. The system includes an effectivereturn path in all hyperlink activations.

[0265] A hyperlinked group 866 is a group element 838 which has anassociated hyperlink, as shown in FIG. 31. When input occurs through anyfield element in the group, the hyperlink 844 associated with the groupis activated. A hyperlinked group can be used to associate hyperlinkbehavior with a field such as a checkbox. It can also be used, inconjunction with the “submit delta” attribute of a form hyperlink, toprovide continuous input to an application. It can therefore be used tosupport a “blackboard” interaction model, i.e. where input is capturedand therefore shared as soon as it occurs.

[0266] 1.7.2 Forms

[0267] A form defines a collection of related input fields used tocapture a related set of inputs through a printed netpage. A form allowsa user to submit one or more parameters to an application softwareprogram running on a server.

[0268] A form 867 is a group element 838 in the document hierarchy. Itultimately contains a set of terminal field elements 839. A forminstance 868 represents a printed instance of a form. It consists of aset of field instances 870 which correspond to the field elements 845 ofthe form. Each field instance has an associated value 871, whose typedepends on the type of the corresponding field element. Each field valuerecords input through a particular printed form instance, i.e. throughone or more printed netpages. The form class diagram is shown in FIG.32.

[0269] Each form instance has a status 872 which indicates whether theform is active, frozen, submitted, void or expired. A form is activewhen first printed. A form becomes frozen once it is signed. A formbecomes submitted once one of its submission hyperlinks has beenactivated, unless the hyperlink has its “submit delta” attribute set. Aform becomes void when the user invokes a void form, reset form orduplicate form page command. A form expires when the time the form hasbeen active exceeds the form's specified lifetime. While the form isactive, form input is allowed. Input through a form which is not activeis instead captured in the background field 833 of the relevant pageinstance. When the form is active or frozen, form submission is allowed.Any attempt to submit a form when the form is not active or frozen isrejected, and instead elicits an form status report.

[0270] Each form instance is associated (at 59) with any form instancesderived from it, thus providing a version history. This allows all butthe latest version of a form in a particular time period to be excludedfrom a search. All input is captured as digital ink. Digital ink 873consists of a set of timestamped stroke groups 874, each of whichconsists of a set of styled strokes 875. Each stroke consists of a setof timestamped pen positions 876, each of which also includes penorientation and nib force. The digital ink class diagram is shown inFIG. 33.

[0271] A field element 845 can be a checkbox field 877, a text field878, a drawing field 879, or a signature field 880. The field elementclass diagram is shown in FIG. 34. Any digital ink captured in a field'szone 58 is assigned to the field.

[0272] A checkbox field has an associated boolean value 881, as shown inFIG. 35. Any mark (a tick, a cross, a stroke, a fill zigzag, etc.)captured in a checkbox field's zone causes a true value to be assignedto the field's value.

[0273] A text field has an associated text value 882, as shown in FIG.36. Any digital ink captured in a text field's zone is automaticallyconverted to text via online handwriting recognition, and the text isassigned to the field's value. Online handwriting recognition iswell-understood (see for example Tappert, C., C. Y. Suen and T.Wakahara, “The State of the Art in On-Line Handwriting Recognition”,IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol.12,No.8, August 1990).

[0274] A signature field has an associated digital signature value 883,as shown in FIG. 37. Any digital ink captured in a signature field'szone is automatically verified with respect to the identity of the ownerof the pen, and a digital signature of the content of the form of whichthe field is part is generated and assigned to the field's value. Thedigital signature is generated using the pen user's private signaturekey specific to the application which owns the form. Online signatureverification is well-understood (see for example Plamondon, R. and G.Lorette, “Automatic Signature Verification and Writer Identification—TheState of the Art”, Pattern Recognition, Vol.22, No.2, 1989).

[0275] A field element is hidden if its “hidden” attribute is set. Ahidden field element does not have an input zone on a page and does notaccept input. It can have an associated field value which is included inthe form data when the form containing the field is submitted.

[0276] “Editing” commands, such as strike-throughs indicating deletion,can also be recognized in form fields.

[0277] Because the handwriting recognition algorithm works “online”(i.e. with access to the dynamics of the pen movement), rather than“offline” (i.e. with access only to a bitmap of pen markings), it canrecognize run-on discretely-written characters with relatively highaccuracy, without a writer-dependent training phase. A writer-dependentmodel of handwriting is automatically generated over time, however, andcan be generated up-front if necessary,

[0278] Digital ink, as already stated, consists of a sequence ofstrokes. Any stroke which starts in a particular element's zone isappended to that element's digital ink stream, ready for interpretation.Any stroke not appended to an object's digital ink stream is appended tothe background field's digital ink stream.

[0279] Digital ink captured in the background field is interpreted as aselection gesture. Circumscription of one or more objects is generallyinterpreted as a selection of the circumscribed objects, although theactual interpretation is application-specific.

[0280] Table 2 summaries these various pen interactions with a netpage.TABLE 2 Summary of pen interactions with a netpage Object Type Pen inputAction Hyperlink General Click Submit action to application Form ClickSubmit form to application Selection Click Submit selection to applica-tion Form field Checkbox Any mark Assign true to field Text HandwritingConvert digital ink to text; assign text to field Drawing Digital inkAssign digital ink to field Signature Signature Verify digital inksignature; generate digital signature of form; assign digital signatureto field None — Circumscription Assign digital ink to current selection

[0281] The system maintains a current selection for each pen. Theselection consists simply of the most recent stroke captured in thebackground field. The selection is cleared after an inactivity timeoutto ensure predictable behavior.

[0282] The raw digital ink captured in every field is retained on thenetpage page server and is optionally transmitted with the form datawhen the form is submitted to the application. This allows theapplication to interrogate the raw digital ink should it suspect theoriginal conversion, such as the conversion of handwritten text. Thiscan, for example, involve human intervention at the application levelfor forms which fail certain application-specific consistency checks. Asan extension to this, the entire background area of a form can bedesignated as a drawing field. The application can then decide, on thebasis of the presence of digital ink outside the explicit fields of theform, to route the form to a human operator, on the assumption that theuser may have indicated amendments to the filled-in fields outside ofthose fields.

[0283]FIG. 38 shows a flowchart of the process of handling pen inputrelative to a netpage. The process consists of receiving (at 884) astroke from the pen; identifying (at 885) the page instance 830 to whichthe page ID 50 in the stroke refers; retrieving (at 886) the pagedescription 5; identifying (at 887) a formatted element 839 whose zone58 the stroke intersects; determining (at 888) whether the formattedelement corresponds to a field element, and if so appending (at 892) thereceived stroke to the digital ink of the field value 871, interpreting(at 893) the accumulated digital ink of the field, and determining (at894) whether the field is part of a hyperlinked group 866 and if soactivating (at 895) the associated hyperlink; alternatively determining(at 889) whether the formatted element corresponds to a hyperlinkelement and if so activating (at 895) the corresponding hyperlink;alternatively, in the absence of an input field or hyperlink, appending(at 890) the received stroke to the digital ink of the background field833; and copying (at 891) the received stroke to the current selection826 of the current pen, as maintained by the registration server.

[0284]FIG. 38a shows a detailed flowchart of step 893 in the processshown in FIG. 38, where the accumulated digital ink of a field isinterpreted according to the type of the field. The process consists ofdetermining (at 896) whether the field is a checkbox and (at 897)whether the digital ink represents a checkmark, and if so assigning (at898) a true value to the field value; alternatively determining (at 899)whether the field is a text field and if so converting (at 900) thedigital ink to computer text, with the help of the appropriateregistration server, and assigning (at 901) the converted computer textto the field value; alternatively determining (at 902) whether the fieldis a signature field and if so verifying (at 903) the digital ink as thesignature of the pen's owner, with the help of the appropriateregistration server, creating (at 904) a digital signature of thecontents of the corresponding form, also with the help of theregistration server and using the pen owner's private signature keyrelating to the corresponding application, and assigning (at 905) thedigital signature to the field value.

[0285] 1.7.3 Page Server Commands

[0286] A page server command is a command which is handled locally bythe page server. It operates directly on form, page and documentinstances.

[0287] A page server command 907 can be a void form command 908, aduplicate form command 909, a reset form command 910, a get form statuscommand 911, a duplicate page command 912, a reset page command 913, aget page status command 914, a duplicate document command 915, a resetdocument command 916, or a get document status command 917, as shown inFIG. 39.

[0288] A void form command voids the corresponding form instance. Aduplicate form command voids the corresponding form instance and thenproduces an active printed copy of the current form instance with fieldvalues preserved. The copy contains the same hyperlink transaction IDsas the original, and so is indistinguishable from the original to anapplication. A reset form command voids the corresponding form instanceand then produces an active printed copy of the form instance with fieldvalues discarded. A get form status command produces a printed report onthe status of the corresponding form instance, including who publishedit, when it was printed, for whom it was printed, and the form status ofthe form instance.

[0289] Since a form hyperlink instance contains a transaction ID, theapplication has to be involved in producing a new form instance. Abutton requesting a new form instance is therefore typically implementedas a hyperlink.

[0290] A duplicate page command produces a printed copy of thecorresponding page instance with the background field value preserved.If the page contains a form or is part of a form, then the duplicatepage command is interpreted as a duplicate form command. A reset pagecommand produces a printed copy of the corresponding page instance withthe background field value discarded. If the page contains a form or ispart of a form, then the reset page command is interpreted as a resetform command. A get page status command produces a printed report on thestatus of the corresponding page instance, including who published it,when it was printed, for whom it was printed, and the status of anyforms it contains or is part of.

[0291] The netpage logo which appears on every netpage is usuallyassociated with a duplicate page element.

[0292] When a page instance is duplicated with field values preserved,field values are printed in their native form, i.e. a checkmark appearsas a standard checkmark graphic, and text appears as typeset text. Onlydrawings and signatures appear in their original form, with a signatureaccompanied by a standard graphic indicating successful signatureverification.

[0293] A duplicate document command produces a printed copy of thecorresponding document instance with background field values preserved.If the document contains any forms, then the duplicate document commandduplicates the forms in the same way a duplicate form command does. Areset document command produces a printed copy of the correspondingdocument instance with background field values discarded. If thedocument contains any forms, then the reset document command resets theforms in the same way a reset form command does. A get document statuscommand produces a printed report on the status of the correspondingdocument instance, including who published it, when it was printed, forwhom it was printed, and the status of any forms it contains.

[0294] If the page server command's “on selected” attribute is set, thenthe command operates on the page identified by the pen's currentselection rather than on the page containing the command. This allows amenu of page server commands to be printed. If the target page doesn'tcontain a page server command element for the designated page servercommand, then the command is ignored.

[0295] An application can provide application-specific handling byembedding the relevant page server command element in a hyperlinkedgroup. The page server activates the hyperlink associated with thehyperlinked group rather than executing the page server command.

[0296] A page server command element is hidden if its “hidden” attributeis set. A hidden command element does not have an input zone on a pageand so cannot be activated directly by a user. It can, however, beactivated via a page server command embedded in a different page, ifthat page server command has its “on selected” attribute set.

[0297] 1.8 Standard Features of Netpages

[0298] In the preferred form, each netpage is printed with the netpagelogo at the bottom to indicate that it is a netpage and therefore hasinteractive properties. The logo also acts as a copy button. In mostcases pressing the logo produces a copy of the page. In the case of aform, the button produces a copy of the entire form. And in the case ofa secure document, such as a ticket or coupon, the button elicits anexplanatory note or advertising page.

[0299] The default single-page copy function is handled directly by therelevant netpage page server. Special copy functions are handled bylinking the logo button to an application.

[0300] 1.9 User Help System

[0301] In a preferred embodiment, the netpage printer has a singlebutton labelled “Help”. When pressed it elicits a single page ofinformation, including:

[0302] status of printer connection

[0303] status of printer consumables

[0304] top-level help menu

[0305] document function menu

[0306] top-level netpage network directory

[0307] The help menu provides a hierarchical manual on how to use thenetpage system.

[0308] The document function menu includes the following functions:

[0309] print a copy of a document

[0310] print a clean copy of a form

[0311] print the status of a document

[0312] A document function is initiated by simply pressing the buttonand then touching any page of the document. The status of a documentindicates who published it and when, to whom it was delivered, and towhom and when it was subsequently submitted as a form.

[0313] The netpage network directory allows the user to navigate thehierarchy of publications and services on the network. As analternative, the user can call the netpage network “900” number “yellowpages” and speak to a human operator. The operator can locate thedesired document and route it to the user's printer. Depending on thedocument type, the publisher or the user pays the small “yellow pages”service fee.

[0314] The help page is obviously unavailable if the printer is unableto print. In this case the “error” light is lit and the user can requestremote diagnosis over the network.

[0315] 2 Personalized Publication Model

[0316] In the following description, news is used as a canonicalpublication example to illustrate personalization mechanisms in thenetpage system. Although news is often used in the limited sense ofnewspaper and newsmagazine news, the intended scope in the presentcontext is wider.

[0317] In the netpage system, the editorial content and the advertisingcontent of a news publication are personalized using differentmechanisms. The editorial content is personalized according to thereader's explicitly stated and implicitly captured interest profile. Theadvertising content is personalized according to the reader's localityand demographic.

[0318] 2.1 Editorial Personalization

[0319] A subscriber can draw on two kinds of news sources: those thatdeliver news publications, and those that deliver news streams. Whilenews publications are aggregated and edited by the publisher, newsstreams are aggregated either by a news publisher or by a specializednews aggregator. News publications typically correspond to traditionalnewspapers and newsmagazines, while news streams can be many and varied:a “raw” news feed from a news service, a cartoon strip, a freelancewriter's column, a friend's bulletin board, or the reader's own e-mail.

[0320] The netpage publication server supports the publication of editednews publications as well as the aggregation of multiple news streams.By handling the aggregation and hence the formatting of news streamsselected directly by the reader, the server is able to place advertisingon pages over which it otherwise has no editorial control.

[0321] The subscriber builds a daily newspaper by selecting one or morecontributing news publications, and creating a personalized version ofeach. The resulting daily editions are printed and bound together into asingle newspaper. The various members of a household typically expresstheir different interests and tastes by selecting different dailypublications and then customizing them.

[0322] For each publication, the reader optionally selects specificsections. Some sections appear daily, while others appear weekly. Thedaily sections available from The New York Times online, for example,include “Page One Plus”, “National”, “International”, “Opinion”,“Business”, “Arts/Living”, “Technology”, and “Sports”. The set ofavailable sections is specific to a publication, as is the defaultsubset.

[0323] The reader can extend the daily newspaper by creating customsections, each one drawing on any number of news streams. Customsections might be created for e-mail and friends' announcements(“Personal”), or for monitoring news feeds for specific topics (“Alerts”or “Clippings”).

[0324] For each section, the reader optionally specifies its size,either qualitatively (e.g. short, medium, or long), or numerically (i.e.as a limit on its number of pages), and the desired proportion ofadvertising, either qualitatively (e.g. high, normal, low, none), ornumerically (i.e. as a percentage).

[0325] The reader also optionally expresses a preference for a largenumber of shorter articles or a small number of longer articles. Eacharticle is ideally written (or edited) in both short and long forms tosupport this preference.

[0326] An article may also be written (or edited) in different versionsto match the expected sophistication of the reader, for example toprovide children's and adults' versions. The appropriate version isselected according to the reader's age. The reader can specify a“reading age” which takes precedence over their biological age.

[0327] The articles which make up each section are selected andprioritized by the editors, and each is assigned a useful lifetime. Bydefault they are delivered to all relevant subscribers, in priorityorder, subject to space constraints in the subscribers' editions.

[0328] In sections where it is appropriate, the reader may optionallyenable collaborative filtering. This is then applied to articles whichhave a sufficiently long lifetime. Each article which qualifies forcollaborative filtering is printed with rating buttons at the end of thearticle. The buttons can provide an easy choice (e.g. “liked” and“disliked’), making it more likely that readers will bother to rate thearticle.

[0329] Articles with high priorities and short lifetimes are thereforeeffectively considered essential reading by the editors and aredelivered to most relevant subscribers.

[0330] The reader optionally specifies a serendipity factor, eitherqualitatively (e.g. do or don't surprise me), or numerically. A highserendipity factor lowers the threshold used for matching duringcollaborative filtering. A high factor makes it more likely that thecorresponding section will be filled to the reader's specified capacity.A different serendipity factor can be specified for different days ofthe week.

[0331] The reader also optionally specifies topics of particularinterest within a section, and this modifies the priorities assigned bythe editors.

[0332] The speed of the reader's Internet connection affects the qualityat which images can be delivered. The reader optionally specifies apreference for fewer images or smaller images or both. If the number orsize of images is not reduced, then images may be delivered at lowerquality (i.e. at lower resolution or with greater compression).

[0333] At a global level, the reader specifies how quantities, dates,times and monetary values are localized. This involves specifyingwhether units are imperial or metric, a local timezone and time format,and a local currency, and whether the localization consist of in situtranslation or annotation. These preferences are derived from thereader's locality by default.

[0334] To reduce reading difficulties caused by poor eyesight, thereader optionally specifies a global preference for a largerpresentation. Both text and images are scaled accordingly, and lessinformation is accommodated on each page.

[0335] The language in which a news publication is published, and itscorresponding text encoding, is a property of the publication and not apreference expressed by the user. However, the netpage system can beconfigured to provide automatic translation services in various guises.

[0336] 2.2 Advertising Localization and Targeting

[0337] The personalization of the editorial content directly affects theadvertising content, because advertising is typically placed to exploitthe editorial context. Travel ads, for example, are more likely toappear in a travel section than elsewhere. The value of the editorialcontent to an advertiser (and therefore to the publisher) lies in itsability to attract large numbers of readers with the right demographics.

[0338] Effective advertising is placed on the basis of locality anddemographics. Locality determines proximity to particular services,retailers etc., and particular interests and concerns associated withthe local community and environment. Demographics determine generalinterests and preoccupations as well as likely spending patterns.

[0339] A news publisher's most profitable product is advertising“space”, a multi-dimensional entity determined by the publication'sgeographic coverage, the size of its readership, its readershipdemographics, and the page area available for advertising.

[0340] In the netpage system, the netpage publication server computesthe approximate multi-dimensional size of a publication's saleableadvertising space on a per-section basis, taking into account thepublication's geographic coverage, the section's readership, the size ofeach reader's section edition, each reader's advertising proportion, andeach reader's demographic.

[0341] In comparison with other media, the netpage system allows theadvertising space to be defined in greater detail, and allows smallerpieces of it to be sold separately. It therefore allows it to be sold atcloser to its true value.

[0342] For example, the same advertising “slot” can be sold in varyingproportions to several advertisers, with individual readers' pagesrandomly receiving the advertisement of one advertiser or another,overall preserving the proportion of space sold to each advertiser.

[0343] The netpage system allows advertising to be linked directly todetailed product information and online purchasing. It therefore raisesthe intrinsic value of the advertising space.

[0344] Because personalization and localization are handledautomatically by netpage publication servers, an advertising aggregatorcan provide arbitrarily broad coverage of both geography anddemographics. The subsequent disaggregation is efficient because it isautomatic. This makes it more cost-effective for publishers to deal withadvertising aggregators than to directly capture advertising. Eventhough the advertising aggregator is taking a proportion of advertisingrevenue, publishers may find the change profit-neutral because of thegreater efficiency of aggregation. The advertising aggregator acts as anintermediary between advertisers and publishers, and may place the sameadvertisement in multiple publications.

[0345] It is worth noting that ad placement in a netpage publication canbe more complex than ad placement in the publication's traditionalcounterpart, because the publication's advertising space is morecomplex. While ignoring the full complexities of negotiations betweenadvertisers, advertising aggregators and publishers, the preferred formof the netpage system provides some automated support for thesenegotiations, including support for automated auctions of advertisingspace. Automation is particularly desirable for the placement ofadvertisements which generate small amounts of income, such as small orhighly localized advertisements.

[0346] Once placement has been negotiated, the aggregator captures andedits the advertisement and records it on a netpage ad server.Correspondingly, the publisher records the ad placement on the relevantnetpage publication server. When the netpage publication server lays outeach user's personalized publication, it picks the relevantadvertisements from the netpage ad server.

[0347] 2.3 User Profiles

[0348] 2.3.1 Information Filtering

[0349] The personalization of news and other publications relies on anassortment of user-specific profile information, including:

[0350] publication customizations

[0351] collaborative filtering vectors

[0352] contact details

[0353] presentation preferences

[0354] The customization of a publication is typicallypublication-specific, and so the customization information is maintainedby the relevant netpage publication server.

[0355] A collaborative filtering vector consists of the user's ratingsof a number of news items. It is used to correlate different users'interests for the purposes of making recommendations. Although there arebenefits to maintaining a single collaborative filtering vectorindependently of any particular publication, there are two reasons whyit is more practical to maintain a separate vector for each publication:there is likely to be more overlap between the vectors of subscribers tothe same publication than between those of subscribers to differentpublications; and a publication is likely to want to present its users'collaborative filtering vectors as part of the value of its brand, notto be found elsewhere. Collaborative filtering vectors are thereforealso maintained by the relevant netpage publication server.

[0356] Contact details, including name, street address, ZIP Code, state,country, telephone numbers, are global by nature, and are maintained bya netpage registration server.

[0357] Presentation preferences, including those for quantities, datesand times, are likewise global and maintained in the same way.

[0358] The localization of advertising relies on the locality indicatedin the user's contact details, while the targeting of advertising relieson personal information such as date of birth, gender, marital status,income, profession, education, or qualitative derivatives such as agerange and income range.

[0359] For those users who choose to reveal personal information foradvertising purposes, the information is maintained by the relevantnetpage registration server. In the absence of such information,advertising can be targeted on the basis of the demographic associatedwith the user's ZIP or ZIP+4 Code.

[0360] Each user, pen, printer, application provider and application isassigned its own unique identifier, and the netpage registration servermaintains the relationships between them, as shown in FIGS. 21, 22, 23and 24. For registration purposes, a publisher is a special kind ofapplication provider, and a publication is a special kind ofapplication.

[0361] Each user 800 may be authorized to use any number of printers802, and each printer may allow any number of users to use it. Each userhas a single default printer (at 66), to which periodical publicationsare delivered by default, whilst pages printed on demand are deliveredto the printer through which the user is interacting. The server keepstrack of which publishers a user has authorized to print to the user'sdefault printer. A publisher does not record the ID of any particularprinter, but instead resolves the ID when it is required.

[0362] When a user subscribes 808 to a publication 807, the publisher806 (i.e. application provider 803) is authorized to print to aspecified printer or the user's default printer. This authorization canbe revoked at any time by the user. Each user may have several pens 801,but a pen is specific to a single user. If a user is authorized to use aparticular printer, then that printer recognizes any of the user's pens.

[0363] The pen ID is used to locate the corresponding user profilemaintained by a particular netpage registration server, via the DNS inthe usual way.

[0364] A Web terminal 809 can be authorized to print on a particularnetpage printer, allowing Web pages and netpage documents encounteredduring Web browsing to be conveniently printed on the nearest netpageprinter.

[0365] The netpage system can collect, on behalf of a printer provider,fees and commissions on income earned through publications printed onthe provider's printers. Such income can include advertising fees,click-through fees, e-commerce commissions, and transaction fees. If theprinter is owned by the user, then the user is the printer provider.

[0366] Each user also has a netpage account 820 which is used toaccumulate micro-debits and credits (such as those described in thepreceding paragraph); contact details 815, including name, address andtelephone numbers; global preferences 816, including privacy, deliveryand localization settings; any number of biometric records 817,containing the user's encoded signature 818, fingerprint 819 etc; ahandwriting model 819 automatically maintained by the system; and SETpayment card accounts 821 with which e-commerce payments can be made.

[0367] 2.3.2 Favorites List

[0368] A netpage user can maintain a list 922 of “favorites”—links touseful documents etc. on the netpage network. The list is maintained bythe system on the user's behalf It is organized as a hierarchy offolders 924, a preferrred embodiment of which is shown in the classdiagram in FIG. 41.

[0369] 2.3.3 History List

[0370] The system maintains a history list 929 on each user's behalf,containing links to documents etc. accessed by the user through thenetpage system. It is organized as a date-ordered list, a preferredembodiment of which is shown in the class diagram in FIG. 42.

[0371] 2.4 Intelligent Page Layout

[0372] The netpage publication server automatically lays out the pagesof each user's personalized publication on a section-by-section basis.Since most advertisements are in the form of pre-formatted rectangles,they are placed on the page before the editorial content.

[0373] The advertising ratio for a section can be achieved with wildlyvarying advertising ratios on individual pages within the section, andthe ad layout algorithm exploits this. The algorithm is configured toattempt to co-locate closely tied editorial and advertising content,such as placing ads for roofing material specifically within thepublication because of a special feature on do-it-yourself roofingrepairs.

[0374] The editorial content selected for the user, including text andassociated images and graphics, is then laid out according to variousaesthetic rules.

[0375] The entire process, including the selection of ads and theselection of editorial content, must be iterated once the layout hasconverged, to attempt to more closely achieve the user's stated sectionsize preference. The section size preference can, however, be matched onaverage over time, allowing significant day-to-day variations. 2.5Document Format

[0376] Once the document is laid out, it is encoded for efficientdistribution and persistent storage on the netpage network.

[0377] The primary efficiency mechanism is the separation of informationspecific to a single user's edition and information shared betweenmultiple users' editions. The specific information consists of the pagelayout. The shared information consists of the objects to which the pagelayout refers, including images, graphics, and pieces of text.

[0378] A text object contains fully-formatted text represented in theExtensible Markup Language (XML) using the Extensible StylesheetLanguage (XSL). XSL provides precise control over text formattingindependently of the region into which the text is being set, which inthis case is being provided by the layout. The text object containsembedded language codes to enable automatic translation, and embeddedhyphenation hints to aid with paragraph formatting.

[0379] An image object encodes an image in the JPEG 2000 wavelet-basedcompressed image format.

[0380] A graphic object encodes a 2D graphic in Scalable Vector Graphics(SVG) format.

[0381] The layout itself consists of a series of placed image andgraphic objects, linked textflow objects through which text objectsflow, hyperlinks and input fields as described above, and watermarkregions. These layout objects are summarized in Table 3. The layout usesa compact format suitable for efficient distribution and storage. TABLE3 Netpage layout objects Layout Format of object Attribute linked objectImage Position — Image object ID JPEG 2000 Graphic Position — Graphicobject ID SVG Textflow Textflow ID — Zone — Optional text object IDXML/XSL Hyperlink Type — Zone — Application ID, etc. — Field Type —Meaning — Zone — Watermark Zone —

[0382] 2.6 Document Distribution

[0383] As described above, for purposes of efficient distribution andpersistent storage on the netpage network, a user-specific page layoutis separated from the shared objects to which it refers.

[0384] When a subscribed publication is ready to be distributed, thenetpage publication server allocates, with the help of the netpage IDserver 12, a unique ID for each page, page instance, document, anddocument instance.

[0385] The server computes a set of optimized subsets of the sharedcontent and creates a multicast channel for each subset, and then tagseach user-specific layout with the names of the multicast channels whichwill carry the shared content used by that layout. The server thenpointcasts each user's layouts to that user's printer via theappropriate page server, and when the pointcasting is complete,multicasts the shared content on the specified channels. After receivingits pointcast, each page server and printer subscribes to the multicastchannels specified in the page layouts. During the multicasts, each pageserver and printer extracts from the multicast streams those objectsreferred to by its page layouts. The page servers persistently archivethe received page layouts and shared content.

[0386] Once a printer has received all the objects to which its pagelayouts refer, the printer re-creates the fully-populated layout andthen rasterizes and prints it.

[0387] Under normal circumstances, the printer prints pages faster thanthey can be delivered. Assuming a quarter of each page is covered withimages, the average page has a size of less than 400 KB. The printer cantherefore hold in excess of 100 such pages in its internal 64 MB memory,allowing for temporary buffers etc. The printer prints at a rate of onepage per second. This is equivalent to 400 KB or about 3 Mbit of pagedata per second, which is similar to the highest expected rate of pagedata delivery over a broadband network.

[0388] Even under abnormal circumstances, such as when the printer runsout of paper, it is likely that the user will be able to replenish thepaper supply before the printer's 100-page internal storage capacity isexhausted.

[0389] However, if the printer's internal memory does fill up, then theprinter will be unable to make use of a multicast when it first occurs.The netpage publication server therefore allows printers to submitrequests for re-multicasts. When a critical number of requests isreceived or a timeout occurs, the server re-multicasts the correspondingshared objects.

[0390] Once a document is printed, a printer can produce an exactduplicate at any time by retrieving its page layouts and contents fromthe relevant page server.

[0391] 2.7 On-Demand Documents

[0392] When a netpage document is requested on demand, it can bepersonalized and delivered in much the same way as a periodical.However, since there is no shared content, delivery is made directly tothe requesting printer without the use of multicast.

[0393] When a non-netpage document is requested on demand, it is notpersonalized, and it is delivered via a designated netpage formattingserver which reformats it as a netpage document. A netpage formattingserver is a special instance of a netpage publication server. Thenetpage formatting server has knowledge of various Internet documentformats, including Adobe's Portable Document Format (PDF), and HypertextMarkup Language (HTML). In the case of HTML, it can make use of thehigher resolution of the printed page to present Web pages in amulti-column format, with a table of contents. It can automaticallyinclude all Web pages directly linked to the requested page. The usercan tune this behavior via a preference.

[0394] The netpage formatting server makes standard netpage behavior,including interactivity and persistence, available on any Internetdocument, no matter what its origin and format. It hides knowledge ofdifferent document formats from both the netpage printer and the netpagepage server, and hides knowledge of the netpage system from Web servers.

[0395] 3 Security

[0396] 3.1 Cryptography

[0397] Cryptography is used to protect sensitive information, both instorage and in transit, and to authenticate parties to a transaction.There are two classes of cryptography in widespread use: secret-keycryptography and public-key cryptography. The netpage network uses bothclasses of cryptography.

[0398] Secret-key cryptography, also referred to as symmetriccryptography, uses the same key to encrypt and decrypt a message. Twoparties wishing to exchange messages must first arrange to securelyexchange the secret key.

[0399] Public-key cryptography, also referred to as asymmetriccryptography, uses two encryption keys. The two keys are mathematicallyrelated in such a way that any message encrypted using one key can onlybe decrypted using the other key. One of these keys is then published,while the other is kept private. The public key is used to encrypt anymessage intended for the holder of the private key. Once encrypted usingthe public key, a message can only be decrypted using the private key.Thus two parties can securely exchange messages without first having toexchange a secret key. To ensure that the private key is secure, it isnormal for the holder of the private key to generate the key pair.

[0400] Public-key cryptography can be used to create a digitalsignature. The holder of the private key can create a known hash of amessage and then encrypt the hash using the private key. Anyone can thenverify that the encrypted hash constitutes the “signature” of the holderof the private key with respect to that particular message by decryptingthe encrypted hash using the public key and verifying the hash againstthe message. If the signature is appended to the message, then therecipient of the message can verify both that the message is genuine andthat it has not been altered in transit.

[0401] To make public-key cryptography work, there has to be a way todistribute public keys which prevents impersonation. This is normallydone using certificates and certificate authorities. A certificateauthority is a trusted third party which authenticates the connectionbetween a public key and someone's identity. The certificate authorityverifies the person's identity by examining identity documents, and thencreates and signs a digital certificate containing the person's identitydetails and public key. Anyone who trusts the certificate authority canuse the public key in the certificate with a high degree of certaintythat it is genuine. They just have to verify that the certificate hasindeed been signed by the certificate authority, whose public key iswell-known.

[0402] In most transaction environments, public-key cryptography is onlyused to create digital signatures and to securely exchange secretsession keys. Secret-key cryptography is used for all other purposes.

[0403] In the following discussion, when reference is made to the securetransmission of information between a netpage printer and a server, whatactually happens is that the printer obtains the server's certificate,authenticates it with reference to the certificate authority, uses thepublic key-exchange key in the certificate to exchange a secret sessionkey with the server, and then uses the secret session key to encrypt themessage data. A session key, by definition, can have an arbitrarilyshort lifetime.

[0404] 3.2 Netpage Printer Security

[0405] Each netpage printer is assigned a pair of unique identifiers attime of manufacture which are stored in read-only memory in the printerand in the netpage registration server database. The first ID 62 ispublic and uniquely identifies the printer on the netpage network. Thesecond ID is secret and is used when the printer is first registered onthe network.

[0406] When the printer connects to the netpage network for the firsttime after installation, it creates a signature public/private key pair.It transmits the secret ID and the public key securely to the netpageregistration server. The server compares the secret ID against theprinter's secret ID recorded in its database, and accepts theregistration if the IDs match. It then creates and signs a certificatecontaining the printer's public ID and public signature key, and storesthe certificate in the registration database.

[0407] The netpage registration server acts as a certificate authorityfor netpage printers, since it has access to secret information allowingit to verify printer identity.

[0408] When a user subscribes to a publication, a record is created inthe netpage registration server database authorizing the publisher toprint the publication to the user's default printer or a specifiedprinter. Every document sent to a printer via a page server is addressedto a particular user and is signed by the publisher using thepublisher's private signature key. The page server verifies, via theregistration database, that the publisher is authorized to deliver thepublication to the specified user. The page server verifies thesignature using the publisher's public key, obtained from thepublisher's certificate stored in the registration database.

[0409] The netpage registration server accepts requests to add printingauthorizations to the database, so long as those requests are initiatedvia a pen registered to the printer.

[0410] 3.3 Netpage Pen Security

[0411] Each netpage pen is assigned a unique identifier at time ofmanufacture which is stored in read-only memory in the pen and in thenetpage registration server database. The pen ID 61 uniquely identifiesthe pen on the netpage network.

[0412] A netpage pen can “know” a number of netpage printers, and aprinter can “know” a number of pens. A pen communicates with a printervia a radio frequency signal whenever it is within range of the printer.Once a pen and printer are registered, they regularly exchange sessionkeys. Whenever the pen transmits digital ink to the printer, the digitalink is always encrypted using the appropriate session key. Digital inkis never transmitted in the clear.

[0413] A pen stores a session key for every printer it knows, indexed byprinter ID, and a printer stores a session key for every pen it knows,indexed by pen ID. Both have a large but finite storage capacity forsession keys, and will forget a session key on a least-recently-usedbasis if necessary.

[0414] When a pen comes within range of a printer, the pen and printerdiscover whether they know each other. If they don't know each other,then the printer determines whether it is supposed to know the pen. Thismight be, for example, because the pen belongs to a user who isregistered to use the printer. If the printer is meant to know the penbut doesn't, then it initiates the automatic pen registration procedure.If the printer isn't meant to know the pen, then it agrees with the pento ignore it until the pen is placed in a charging cup, at which time itinitiates the registration procedure.

[0415] In addition to its public ID, the pen contains a secretkey-exchange key. The key-exchange key is also recorded in the netpageregistration server database at time of manufacture. Duringregistration, the pen transmits its pen ID to the printer, and theprinter transmits the pen ID to the netpage registration server. Theserver generates a session key for the printer and pen to use, andsecurely transmits the session key to the printer. It also transmits acopy of the session key encrypted with the pen's key-exchange key. Theprinter stores the session key internally, indexed by the pen ID, andtransmits the encrypted session key to the pen. The pen stores thesession key internally, indexed by the printer ID.

[0416] Although a fake pen can impersonate a pen in the pen registrationprotocol, only a real pen can decrypt the session key transmitted by theprinter.

[0417] When a previously unregistered pen is first registered, it is oflimited use until it is linked to a user. A registered but “un-owned”pen is only allowed to be used to request and fill in netpage user andpen registration forms, to register a new user to which the new pen isautomatically linked, or to add a new pen to an existing user.

[0418] The pen uses secret-key rather than public-key encryption becauseof hardware performance constraints in the pen.

[0419] 3.4 Secure Documents

[0420] The netpage system supports the delivery of secure documents suchas tickets and coupons. The netpage printer includes a facility to printwatermarks, but will only do so on request from publishers who aresuitably authorized. The publisher indicates its authority to printwatermarks in its certificate, which the printer is able toauthenticate.

[0421] The “watermark” printing process uses an alternative dithermatrix in specified “watermark” regions of the page. Back-to-back pagescontain mirror-image watermark regions which coincide when printed. Thedither matrices used in odd and even pages' watermark regions aredesigned to produce an interference effect when the regions are viewedtogether, achieved by looking through the printed sheet.

[0422] The effect is similar to a watermark in that it is not visiblewhen looking at only one side of the page, and is lost when the page iscopied by normal means.

[0423] Pages of secure documents cannot be copied using the built-innetpage copy mechanism described in Section 1.9 above. This extends tocopying netpages on netpage-aware photocopiers.

[0424] Secure documents are typically generated as part of e-commercetransactions. They can therefore include the user's photograph which wascaptured when the user registered biometric information with the netpageregistration server, as described in Section 2.

[0425] When presented with a secure netpage document, the recipient canverify its authenticity by requesting its status in the usual way. Theunique ID of a secure document is only valid for the lifetime of thedocument, and secure document IDs are allocated non-contiguously toprevent their prediction by opportunistic forgers. A secure documentverification pen can be developed with built-in feedback on verificationfailure, to support easy point-of-presentation document verification.

[0426] Clearly neither the watermark nor the user's photograph aresecure in a cryptographic sense. They simply provide a significantobstacle to casual forgery. Online document verification, particularlyusing a verification pen, provides an added level of security where itis needed, but is still not entirely immune to forgeries.

[0427] 3.5 Non-Repudiation

[0428] In the netpage system, forms submitted by users are deliveredreliably to forms handlers and are persistently archived on netpage pageservers. It is therefore impossible for recipients to repudiatedelivery.

[0429] E-commerce payments made through the system, as described inSection 4, are also impossible for the payee to repudiate.

[0430] 4 Electronic Commerce Model

[0431] 4.1 Secure Electronic Transaction (Set)

[0432] The netpage system uses the Secure Electronic Transaction (SET)system as one of its payment systems. SET, having been developed byMasterCard and Visa, is organized around payment cards, and this isreflected in the terminology. However, much of the system is independentof the type of accounts being used.

[0433] In SET, cardholders and merchants register with a certificateauthority and are issued with certificates containing their publicsignature keys. The certificate authority verifies a cardholder'sregistration details with the card issuer as appropriate, and verifies amerchant's registration details with the acquirer as appropriate.Cardholders and merchants store their respective private signature keyssecurely on their computers. During the payment process, thesecertificates are used to mutually authenticate a merchant andcardholder, and to authenticate them both to the payment gateway.

[0434] SET has not yet been adopted widely, partly because cardholdermaintenance of keys and certificates is considered burdensome. Interimsolutions which maintain cardholder keys and certificates on a serverand give the cardholder access via a password have met with somesuccess.

[0435] 4.2 Set Payments

[0436] In the netpage system the netpage registration server acts as aproxy for the netpage user (i.e. the cardholder) in SET paymenttransactions.

[0437] The netpage system uses biometrics to authenticate the user andauthorize SET payments. Because the system is pen-based, the biometricused is the user's on-line signature, consisting of time-varying penposition and pressure. A fingerprint biometric can also be used bydesigning a fingerprint sensor into the pen, although at a higher cost.The type of biometric used only affects the capture of the biometric,not the authorization aspects of the system.

[0438] The first step to being able to make SET payments is to registerthe user's biometric with the netpage registration server. This is donein a controlled environment, for example a bank, where the biometric canbe captured at the same time as the user's identity is verified. Thebiometric is captured and stored in the registration database, linked tothe user's record. The user's photograph is also optionally captured andlinked to the record. The SET cardholder registration process iscompleted, and the resulting private signature key and certificate arestored in the database. The user's payment card information is alsostored, giving the netpage registration server enough information to actas the user's proxy in any SET payment transaction.

[0439] When the user eventually supplies the biometric to complete apayment, for example by signing a netpage order form, the printersecurely transmits the order information, the pen ID and the biometricdata to the netpage registration server. The server verifies thebiometric with respect to the user identified by the pen ID, and fromthen on acts as the user's proxy in completing the SET paymenttransaction.

[0440] 4.3 Micro-Payments

[0441] The netpage system includes a mechanism for micro-payments, toallow the user to be conveniently charged for printing low-costdocuments on demand and for copying copyright documents, and possiblyalso to allow the user to be reimbursed for expenses incurred inprinting advertising material. The latter depends on the level ofsubsidy already provided to the user.

[0442] When the user registers for e-commerce, a network account isestablished which aggregates micro-payments. The user receives astatement on a regular basis, and can settle any outstanding debitbalance using the standard payment mechanism.

[0443] The network account can be extended to aggregate subscriptionfees for periodicals, which would also otherwise be presented to theuser in the form of individual statements.

[0444] 4.4 Transactions

[0445] When a user requests a netpage in a particular applicationcontext, the application is able to embed a user-specific transaction ID55 in the page. Subsequent input through the page is tagged with thetransaction ID, and the application is thereby able to establish anappropriate context for the user's input.

[0446] When input occurs through a page which is not user-specific,however, the application must use the user's unique identity toestablish a context. A typical example involves adding items from apre-printed catalog page to the user's virtual “shopping cart”. Toprotect the user's privacy, however, the unique user ID 60 known to thenetpage system is not divulged to applications. This is to preventdifferent application providers from easily correlating independentlyaccumulated behavioral data.

[0447] The netpage registration server instead maintains an anonymousrelationship between a user and an application via a unique alias ID 65,as shown in FIG. 24. Whenever the user activates a hyperlink tagged withthe “registered” attribute, the netpage page server asks the netpageregistration server to translate the associated application ID 64,together with the pen ID 61, into an alias ID 65. The alias ID is thensubmitted to the hyperlink's application.

[0448] The application maintains state information indexed by alias ID,and is able to retrieve user-specific state information withoutknowledge of the global identity of the user.

[0449] The system also maintains an independent certificate and privatesignature key for each of a user's applications, to allow it to signapplication transactions on behalf of the user using onlyapplication-specific information.

[0450] To assist the system in routing product bar code (UPC)“hyperlink” activations, the system records a favorite application onbehalf of the user for any number of product types.

[0451] Each application is associated with an application provider, andthe system maintains an account on behalf of each application provider,to allow it to credit and debit the provider for click-through fees etc.

[0452] An application provider can be a publisher of periodicalsubscribed content. The system records the user's willingness to receivethe subscribed publication, as well as the expected frequency ofpublication.

[0453] 4.5 Resource Descriptions and Copyright

[0454] A preferred embodiment of a resource description class diagram isshown in FIG. 40.

[0455] Each document and content object may be described by one or moreresource descriptions 842.

[0456] Resource descriptions use the Dublin Core metadata element set,which is designed to facilitate discovery of electronic resources.Dublin Core metadata conforms to the World Wide Web Consortium (W3C)Resource Description Framework (RDF).

[0457] A resource description may identify rights holders 920. Thenetpage system automatically transfers copyright fees from users torights holders when users print copyright content.

[0458] 5 Communications Protocols

[0459] A communications protocol defines an ordered exchange of messagesbetween entities. In the netpage system, entities such as pens, printersand servers utilise a set of defined protocols to cooperatively handleuser interaction with the netpage system.

[0460] Each protocol is illustrated by way of a sequence diagram inwhich the horizontal dimension is used to represent message flow and thevertical dimension is used to represent time. Each entity is representedby a rectangle containing the name of the entity and a vertical columnrepresenting the lifeline of the entity. During the time an entityexists, the lifeline is shown as a dashed line. During the time anentity is active, the lifeline is shown as a double line. Because theprotocols considered here do not create or destroy entities, lifelinesare generally cut short as soon as an entity ceases to participate in aprotocol.

[0461] 5.1 Subscription Delivery Protocol

[0462] A preferred embodiment of a subscription delivery protocol isshown in FIG. 43.

[0463] A large number of users may subscribe to a periodicalpublication. Each user's edition may be laid out differently, but manyusers' editions will share common content such as text objects and imageobjects. The subscription delivery protocol therefore delivers documentstructures to individual printers via pointcast, but delivers sharedcontent objects via multicast.

[0464] The application (i.e. publisher) first obtains a document ID 51for each document from an ID server 12. It then sends each documentstructure, including its document ID and page descriptions, to the pageserver 10 responsible for the document's newly allocated ID. It includesits own application ID 64, the subscriber's alias ID 65, and therelevant set of multicast channel names. It signs the message using itsprivate signature key.

[0465] The page server uses the application ID and alias ID to obtainfrom the registration server the corresponding user ID 60, the user'sselected printer ID 62 (which may be explicitly selected for theapplication, or may be the user's default printer), and theapplication's certificate.

[0466] The application's certificate allows the page server to verifythe message signature. The page server's request to the registrationserver fails if the application ID and alias ID don't together identifya subscription 808.

[0467] The page server then allocates document and page instance IDs andforwards the page descriptions, including page IDs 50, to the printer.It includes the relevant set of multicast channel names for the printerto listen to.

[0468] It then returns the newly allocated page IDs to the applicationfor future reference.

[0469] Once the application has distributed all of the documentstructures to the subscribers' selected printers via the relevant pageservers, it multicasts the various subsets of the shared objects on thepreviously selected multicast channels. Both page servers and printersmonitor the appropriate multicast channels and receive their requiredcontent objects. They are then able to populate the previously pointcastdocument structures. This allows the page servers to add completedocuments to their databases, and it allows the printers to print thedocuments.

[0470] 5.2 Hyperlink Activation Protocol

[0471] A preferred embodiment of a hyperlink activation protocol isshown in FIG. 45.

[0472] When a user clicks on a netpage with a netpage pen, the pencommunicates the click to the nearest netpage printer 601. The clickidentifies the page and a location on the page. The printer alreadyknows the ID 61 of the pen from the pen connection protocol.

[0473] The printer determines, via the DNS, the network address of thepage server 10 a handling the particular page ID 50. The address mayalready be in its cache if the user has recently interacted with thesame page. The printer then forwards the pen ID, its own printer ID 62,the page ID and click location to the page server.

[0474] The page server loads the page description 5 identified by thepage ID and determines which input element's zone 58, if any, the clicklies in. Assuming the relevant input element is a hyperlink element 844,the page server then obtains the associated application ID 64 and linkID 54, and determines, via the DNS, the network address of theapplication server hosting the application 71.

[0475] The page server uses the pen ID 61 to obtain the correspondinguser ID 60 from the registration server 11, and then allocates aglobally unique hyperlink request ID 52 and builds a hyperlink request934. The hyperlink request class diagram is shown in FIG. 44. Thehyperlink request records the IDs of the requesting user and printer,and identifies the clicked hyperlink instance 862. The page server thensends its own server ID 53, the hyperlink request ID, and the link ID tothe application.

[0476] The application produces a response document according toapplication-specific logic, and obtains a document ID 51 from an IDserver 12. It then sends the document to the page server 10 bresponsible for the document's newly allocated ID, together with therequesting page server's ID and the hyperlink request ID.

[0477] The second page server sends the hyperlink request ID andapplication ID to the first page server to obtain the corresponding userID and printer ID 62. The first page server rejects the request if thehyperlink request has expired or is for a different application.

[0478] The second page server allocates document instance and page IDs50, returns the newly allocated page IDs to the application, adds thecomplete document to its own database, and finally sends the pagedescriptions to the requesting printer.

[0479] The hyperlink instance may include a meaningful transaction ID55, in which case the first page server includes the transaction ID inthe message sent to the application. This allows the application toestablish a transaction-specific context for the hyperlink activation.

[0480] If the hyperlink requires a user alias, i.e. its “alias required”attribute is set, then the first page server sends both the pen ID 61and the hyperlink's application ID 64 to the registration server 11 toobtain not just the user ID corresponding to the pen ID but also thealias ID 65 corresponding to the application ID and the user ID. Itincludes the alias ID in the message sent to the application, allowingthe application to establish a user-specific context for the hyperlinkactivation.

[0481]5.3 Handwriting Recognition Protocol

[0482] When a user draws a stroke on a netpage with a netpage pen, thepen communicates the stroke to the nearest netpage printer. The strokeidentifies the page and a path on the page.

[0483] The printer forwards the pen ID 61, its own printer ID 62, thepage ID 50 and stroke path to the page server 10 in the usual way.

[0484] The page server loads the page description 5 identified by thepage ID and determines which input element's zone 58, if any, the strokeintersects. Assuming the relevant input element is a text field 878, thepage server appends the stroke to the text field's digital ink.

[0485] After a period of inactivity in the zone of the text field, thepage server sends the pen ID and the pending strokes to the registrationserver 11 for interpretation. The registration server identifies theuser corresponding to the pen, and uses the user's accumulatedhandwriting model 822 to interpret the strokes as handwritten text. Onceit has converted the strokes to text, the registration server returnsthe text to the requesting page server. The page server appends the textto the text value of the text field.

[0486]5.4 Signature Verification Protocol

[0487] Assuming the input element whose zone the stroke intersects is asignature field 880, the page server 10 appends the stroke to thesignature field's digital ink.

[0488] After a period of inactivity in the zone of the signature field,the page server sends the pen ID 61 and the pending strokes to theregistration server 11 for verification. It also sends the applicationID 64 associated with the form of which the signature field is part, aswell as the form ID 56 and the current data content of the form. Theregistration server identifies the user corresponding to the pen, anduses the user's dynamic signature biometric 818 to verify the strokes asthe user's signature. Once it has verified the signature, theregistration server uses the application ID 64 and user ID 60 toidentify the user's application-specific private signature key. It thenuses the key to generate a digital signature of the form data, andreturns the digital signature to the requesting page server. The pageserver assigns the digital signature to the signature field and sets theassociated form's status to frozen.

[0489] The digital signature includes the alias ID 65 of thecorresponding user. This allows a single form to capture multiple users'signatures.

[0490] 5.5 Form Submission Protocol

[0491] A preferred embodiment of a form submission protocol is shown inFIG. 46.

[0492] Form submission occurs via a form hyperlink activation. It thusfollows the protocol defined in Section 5.2, with some form-specificadditions.

[0493] In the case of a form hyperlink, the hyperlink activation messagesent by the page server 10 to the application 71 also contains the formID 56 and the current data content of the form. If the form contains anysignature fields, then the application verifies each one by extractingthe alias ID 65 associated with the corresponding digital signature andobtaining the corresponding certificate from the registration server 11.

[0494] 5.6 Commission Payment Protocol

[0495] A preferred embodiment of a commission payment protocol is shownin FIG. 47.

[0496] In an e-commerce environment, fees and commissions may be payablefrom an application provider to a publisher on click-throughs,transactions and sales. Commissions on fees and commissions oncommissions may also be payable from the publisher to the provider ofthe printer. The hyperlink request ID 52 is used to route a fee orcommission credit from the target application provider 70 a (e.g.merchant) to the source application provider 70 b (i.e. publisher), andfrom the source application provider 70 b to the printer provider 72.

[0497] The target application receives the hyperlink request ID from thepage server 10 when the hyperlink is first activated, as described inSection 5.2. When the target application needs to credit the sourceapplication provider, it sends the application provider credit to theoriginal page server together with the hyperlink request ID. The pageserver uses the hyperlink request ID to identify the source application,and sends the credit on to the relevant registration server 11 togetherwith the source application ID 64, its own server ID 53, and thehyperlink request ID. The registration server credits the correspondingapplication provider's account 827. It also notifies the applicationprovider.

[0498] If the application provider needs to credit the printer provider,it sends the printer provider credit to the original page servertogether with the hyperlink request ID. The page server uses thehyperlink request ID to identify the printer, and sends the credit on tothe relevant registration server together with the printer ID. Theregistration server credits the corresponding printer provider account814.

[0499] The source application provider is optionally notified of theidentity of the target application provider, and the printer provider ofthe identity of the source application provider.

[0500] 6. Netpage Pen Description

[0501] 6.1 Pen Mechanics

[0502] Referring to FIGS. 8 and 9, the pen, generally designated byreference numeral 101, includes a housing 102 in the form of a plasticsmoulding having walls 103 defining an interior space 104 for mountingthe pen components. The pen top 105 is in operation rotatably mounted atone end 106 of the housing 102. A semi-transparent cover 107 is securedto the opposite end 108 of the housing 102. The cover 107 is also ofmoulded plastics, and is formed from semi-transparent material in orderto enable the user to view the status of the LED mounted within thehousing 102. The cover 107 includes a main part 109 which substantiallysurrounds the end 108 of the housing 102 and a projecting portion 110which projects back from the main part 109 and fits within acorresponding slot 111 formed in the walls 103 of the housing 102. Aradio antenna 112 is mounted behind the projecting portion 110, withinthe housing 102. Screw threads 113 surrounding an aperture 113A on thecover 107 are arranged to receive a metal end piece 114, includingcorresponding screw threads 115. The metal end piece 114 is removable toenable ink cartridge replacement.

[0503] Also mounted within the cover 107 is a tri-color status LED 116on a flex PCB 117. The antenna 112 is also mounted on the flex PCB 117.The status LED 116 is mounted at the top of the pen 101 for goodall-around visibility.

[0504] The pen can operate both as a normal marking ink pen and as anon-marking stylus. An ink pen cartridge 118 with nib 119 and a stylus120 with stylus nib 121 are mounted side by side within the housing 102.Either the ink cartridge nib 119 or the stylus nib 121 can be broughtforward through open end 122 of the metal end piece 114, by rotation ofthe pen top 105. Respective slider blocks 123 and 124 are mounted to theink cartridge 118 and stylus 120, respectively. A rotatable cam barrel125 is secured to the pen top 105 in operation and arranged to rotatetherewith. The cam barrel 125 includes a cam 126 in the form of a slotwithin the walls 181 of the cam barrel. Cam followers 127 and 128projecting from slider blocks 123 and 124 fit within the cam slot 126.On rotation of the cam barrel 125, the slider blocks 123 or 124 moverelative to each other to project either the pen nib 119 or stylus nib121 out through the hole 122 in the metal end piece 114. The pen 101 hasthree states of operation. By turning the top 105 through 900 steps, thethree states are:

[0505] Stylus 120 nib 121 out;

[0506] Ink cartridge 118 nib 119 out; and

[0507] Neither ink cartridge 118 nib 119 out nor stylus 120 nib 121 out.

[0508] A second flex PCB 129, is mounted on an electronics chassis 130which sits within the housing 102. The second flex PCB 129 mounts aninfrared LED 131 for providing infrared radiation for projection ontothe surface. An image sensor 132 is provided mounted on the second flexPCB 129 for receiving reflected radiation from the surface. The secondflex PCB 129 also mounts a radio frequency chip 133, which includes anRF transmitter and RF receiver, and a controller chip 134 forcontrolling operation of the pen 101. An optics block 135 (formed frommoulded clear plastics) sits within the cover 107 and projects aninfrared beam onto the surface and receives images onto the image sensor132. Power supply wires 136 connect the components on the second flexPCB 129 to battery contacts 137 which are mounted within the cam barrel125. A terminal 138 connects to the battery contacts 137 and the cambarrel 125. A three volt rechargeable battery 139 sits within the cambarrel 125 in contact with the battery contacts. An induction chargingcoil 140 is mounted about the second flex PCB 129 to enable rechargingof the battery 139 via induction. The second flex PCB 129 also mounts aninfrared LED 143 and infrared photodiode 144 for detecting displacementin the cam barrel 125 when either the stylus 120 or the ink cartridge118 is used for writing, in order to enable a determination of the forcebeing applied to the surface by the pen nib 119 or stylus nib 121. TheIR photodiode 144 detects light from the IR LED 143 via reflectors (notshown) mounted on the slider blocks 123 and 124.

[0509] Rubber grip pads 141 and 142 are provided towards the end 108 ofthe housing 102 to assist gripping the pen 101, and top 105 alsoincludes a clip 142 for clipping the pen 101 to a pocket.

[0510] 6.2 Pen Controller

[0511] The pen 101 is arranged to determine the position of its nib(stylus nib 121 or ink cartridge nib 119) by imaging, in the infraredspectrum, an area of the surface in the vicinity of the nib. It recordsthe location data from the nearest location tag, and is arranged tocalculate the distance of the nib 121 or 119 from the location tabutilising optics 135 and controller chip 134. The controller chip 134calculates the orientation of the pen and the nib-to-tag distance fromthe perspective distortion observed on the imaged tag.

[0512] Utilising the RF chip 133 and antenna 112 the pen 101 cantransmit the digital ink data (which is encrypted for security andpackaged for efficient transmission) to the computing system.

[0513] When the pen is in range of a receiver, the digital ink data istransmitted as it is formed. When the pen 101 moves out of range,digital ink data is buffered within the pen 101 (the pen 101 circuitryincludes a buffer arranged to store digital ink data for approximately12 minutes of the pen motion on the surface) and can be transmittedlater.

[0514] The controller chip 134 is mounted on the second flex PCB 129 inthe pen 101. FIG. 10 is a block diagram illustrating in more detail thearchitecture of the controller chip 134. FIG. 10 also showsrepresentations of the RF chip 133, the image sensor 132, the tri-colorstatus LED 116, the IR illumination LED 131, the IR force sensor LED143, and the force sensor photodiode 144.

[0515] The pen controller chip 134 includes a controlling processor 145.Bus 146 enables the exchange of data between components of thecontroller chip 134. Flash memory 147 and a 512 KB DRAM 148 are alsoincluded. An analog-to-digital converter 149 is arranged to convert theanalog signal from the force sensor photodiode 144 to a digital signal.

[0516] An image sensor interface 152 interfaces with the image sensor132. A transceiver controller 153 and base band circuit 154 are alsoincluded to interface with the RF chip 133 which includes an RF circuit155 and RF resonators and inductors 156 connected to the antenna 112.

[0517] The controlling processor 145 captures and decodes location datafrom tags from the surface via the image sensor 132, monitors the forcesensor photodiode 144, controls the LEDs 116, 131 and 143, and handlesshort-range radio communication via the radio transceiver 153. It is amedium-performance (˜40 MHz) general-purpose RISC processor.

[0518] The processor 145, digital transceiver components (transceivercontroller 153 and baseband circuit 154), image sensor interface 152,flash memory 147 and 512 KB DRAM 148 are integrated in a singlecontroller ASIC. Analog RF components (RF circuit 155 and RF resonatorsand inductors 156) are provided in the separate RF chip.

[0519] The image sensor is a 215×215 pixel CCD (such a sensor isproduced by Matsushita Electronic Corporation, and is described in apaper by Itakura, K T Nobusada, N Okusenya, R Nagayoshi, and M Ozaki, “A1 mm 50k-Pixel IT CCD Image Sensor for Miniature Camera System”, IEEETransactions on Electronic Devices, Volt 47, number 1, January 2000,which is incorporated herein by reference) with an IR filter.

[0520] The controller ASIC 134 enters a quiescent state after a periodof inactivity when the pen 101 is not in contact with a surface. Itincorporates a dedicated circuit 150 which monitors the force sensorphotodiode 144 and wakes up the controller 134 via the power manager 151on a pen-down event.

[0521] The radio transceiver communicates in the unlicensed 900 MHz bandnormally used by cordless telephones, or alternatively in the unlicensed2.4 GHz industrial, scientific and medical (ISM) band, and usesfrequency hopping and collision detection to provide interference-freecommunication.

[0522] In an alternative embodiment, the pen incorporates an InfraredData Association (IrDA) interface for short-range communication with abase station or netpage printer.

[0523] In a further embodiment, the pen 101 includes a pair oforthogonal accelerometers mounted in the normal plane of the pen 101axis. The accelerometers 190 are shown in FIGS. 9 and 10 in ghostoutline.

[0524] The provision of the accelerometers enables this embodiment ofthe pen 101 to sense motion without reference to surface location tags,allowing the location tags to be sampled at a lower rate. Each locationtag ID can then identify an object of interest rather than a position onthe surface. For example, if the object is a user interface inputelement (e.g. a command button), then the tag ID of each location tagwithin the area of the input element can directly identify the inputelement.

[0525] The acceleration measured by the accelerometers in each of the xand y directions is integrated with respect to time to produce aninstantaneous velocity and position.

[0526] Since the starting position of the stroke is not known, onlyrelative positions within a stroke are calculated. Although positionintegration accumulates errors in the sensed acceleration,accelerometers typically have high resolution, and the time duration ofa stroke, over which errors accumulate, is short.

[0527] 7. Netpage Printer Description

[0528] 7.1 Printer Mechanics

[0529] The vertically-mounted netpage wallprinter 601 is shown fullyassembled in FIG. 11. It prints netpages on Letter/A4 sized media usingduplexed 8½″ Memjet™ print engines 602 and 603, as shown in FIGS. 12 and12a. It uses a straight paper path with the paper 604 passing throughthe duplexed print engines 602 and 603 which print both sides of a sheetsimultaneously, in full color and with full bleed.

[0530] An integral binding assembly 605 applies a strip of glue alongone edge of each printed sheet, allowing it to adhere to the previoussheet when pressed against it. This creates a final bound document 618which can range in thickness from one sheet to several hundred sheets.

[0531] The replaceable ink cartridge 627, shown in FIG. 13 coupled withthe duplexed print engines, has bladders or chambers for storingfixative, adhesive, and cyan, magenta, yellow, black and infrared inks.The cartridge also contains a micro air filter in a base molding. Themicro air filter interfaces with an air pump 638 inside the printer viaa hose 639. This provides filtered air to the printheads to preventingress of micro particles into the Memjet™ printheads 350 which mightotherwise clog the printhead nozzles. By incorporating the air filterwithin the cartridge, the operational life of the filter is effectivelylinked to the life of the cartridge. The ink cartridge is a fullyrecyclable product with a capacity for printing and gluing 3000 pages(1500 sheets).

[0532] Referring to FIG. 12, the motorized media pick-up roller assembly626 pushes the top sheet directly from the media tray past a papersensor on the first print engine 602 into the duplexed Memjet™ printheadassembly. The two Memjet™ print engines 602 and 603 are mounted in anopposing in-line sequential configuration along the straight paper path.The paper 604 is drawn into the first print engine 602 by integral,powered pick-up rollers 626. The position and size of the paper 604 issensed and full bleed printing commences. Fixative is printedsimultaneously to aid drying in the shortest possible time.

[0533] The paper exits the first Memjet™ print engine 602 through a setof powered exit spike wheels (aligned along the straight paper path),which act against a rubberized roller. These spike wheels contact the‘wet’ printed surface and continue to feed the sheet 604 into the secondMemjet™ print engine 603.

[0534] Referring to FIGS. 12 and 12a, the paper 604 passes from theduplexed print engines 602 and 603 into the binder assembly 605. Theprinted page passes between a powered spike wheel axle 670 with afibrous support roller and another movable axle with spike wheels and amomentary action glue wheel. The movable axle/glue assembly 673 ismounted to a metal support bracket and it is transported forward tointerface with the powered axle 670 via gears by action of a camshaft. Aseparate motor powers this camshaft.

[0535] The glue wheel assembly 673 consists of a partially hollow axle679 with a rotating coupling for the glue supply hose 641 from the inkcartridge 627. This axle 679 connects to a glue wheel, which absorbsadhesive by capillary action through radial holes. A molded housing 682surrounds the glue wheel, with an opening at the front. Pivoting sidemoldings and sprung outer doors are attached to the metal bracket andhinge out sideways when the rest of the assembly 673 is thrust forward.This action exposes the glue wheel through the front of the moldedhousing 682. Tension springs close the assembly and effectively cap theglue wheel during periods of inactivity.

[0536] As the sheet 604 passes into the glue wheel assembly 673,adhesive is applied to one vertical edge on the front side (apart fromthe first sheet of a document) as it is transported down into thebinding assembly 605.

[0537] 7.2 Printer Controller Architecture

[0538] The netpage printer controller consists of a controllingprocessor 750, a factory-installed or field-installed network interfacemodule 625, a radio transceiver (transceiver controller 753, basebandcircuit 754, RF circuit 755, and RF resonators and inductors 756), dualraster image processor (RIP) DSPs 757, duplexed print engine controllers760 a and 760 b, flash memory 658, and 64 MB of DRAM 657, as illustratedin FIG. 14.

[0539] The controlling processor handles communication with the network19 and with local wireless netpage pens 101, senses the help button 617,controls the user interface LEDs 613-616, and feeds and synchronizes theRIP DSPs 757 and print engine controllers 760. It consists of amedium-performance general-purpose microprocessor. The controllingprocessor 750 communicates with the print engine controllers 760 via ahigh-speed serial bus 659.

[0540] The RIP DSPs rasterize and compress page descriptions to thenetpage printer's compressed page format. Each print engine controllerexpands, dithers and prints page images to its associated Memjet™printhead 350 in real time (i.e. at over 30 pages per minute). Theduplexed print engine controllers print both sides of a sheetsimultaneously.

[0541] The master print engine controller 760 a controls the papertransport and monitors ink usage in conjunction with the master QA chip665 and the ink cartridge QA chip 761. The printer controller's flashmemory 658 holds the software for both the processor 750 and the DSPs757, as well as configuration data. This is copied to main memory 657 atboot time.

[0542] The processor 750, DSPs 757, and digital transceiver components(transceiver controller 753 and baseband circuit 754) are integrated ina single controller ASIC 656. Analog RF components (RF circuit 755 andRF resonators and inductors 756) are provided in a separate RF chip 762.The network interface module 625 is separate, since netpage printersallow the network connection to be factory-selected or field-selected.Flash memory 658 and the 2×256 Mbit (64 MB) DRAM 657 is also off-chip.The print engine controllers 760 are provided in separate ASICs.

[0543] A variety of network interface modules 625 are provided, eachproviding a netpage network interface 751 and optionally a localcomputer or network interface 752. Netpage network Internet interfacesinclude POTS modems, Hybrid Fiber-Coax (HFC) cable modems, ISDN modems,DSL modems, satellite transceivers, current and next-generation cellulartelephone transceivers, and wireless local loop (WLL) transceivers.Local interfaces include IEEE 1284 (parallel port), 10Base-T and100Base-T Ethernet, USB and USB 2.0, IEEE 1394 (Firewire), and variousemerging home networking interfaces.

[0544] If an Internet connection is available on the local network, thenthe local network interface can be used as the netpage networkinterface.

[0545] The radio transceiver 753 communicates in the unlicensed 900 MHzband normally used by cordless telephones, or alternatively in theunlicensed 2.4 GHz industrial, scientific and medical (ISM) band, anduses frequency hopping and collision detection to provideinterference-free communication.

[0546] The printer controller optionally incorporates an Infrared DataAssociation (IrDA) interface for receiving data “squirted” from devicessuch as netpage cameras. In an alternative embodiment, the printer usesthe IrDA interface for short-range communication with suitablyconfigured netpage pens.

[0547] 7.2.1 Rasterization and Printing

[0548] Once the main processor 750 has received and verified thedocument's page layouts and page objects, it runs the appropriate RIPsoftware on the DSPs 757.

[0549] The DSPs 757 rasterize each page description and compress therasterized page image. The main processor stores each compressed pageimage in memory. The simplest way to load-balance multiple DSPs is tolet each DSP rasterize a separate page. The DSPs can always be kept busysince an arbitrary number of rasterized pages can, in general, be storedin memory. This strategy only leads to potentially poor DSP utilizationwhen rasterizing short documents.

[0550] Watermark regions in the page description are rasterized to acontone-resolution bi-level bitmap which is losslessly compressed tonegligible size and which forms part of the compressed page image.

[0551] The infrared (IR) layer of the printed page contains codednetpage tags at a density of about six per inch. Each tag encodes thepage ID, tag ID, and control bits, and the data content of each tag isgenerated during rasterization and stored in the compressed page image.

[0552] The main processor 750 passes back-to-back page images to theduplexed print engine controllers 760. Each print engine controller 760stores the compressed page image in its local memory, and starts thepage expansion and printing pipeline. Page expansion and printing ispipelined because it is impractical to store an entire 114 MB bi-levelCMYK+IR page image in memory.

[0553] 7.2.2 Print Engine Controller

[0554] The page expansion and printing pipeline of the print enginecontroller 760 consists of a high speed IEEE 1394 serial interface 659,a standard JPEG decoder 763, a standard Group 4 Fax decoder 764, acustom halftoner/compositor unit 765, a custom tag encoder 766, a lineloader/formatter unit 767, and a custom interface 768 to the Memjet™printhead 350.

[0555] The print engine controller 360 operates in a double bufferedmanner. While one page is loaded into DRAM 769 via the high speed serialinterface 659, the previously loaded page is read from DRAM 769 andpassed through the print engine controller pipeline. Once the page hasfinished printing, the page just loaded is printed while another page isloaded.

[0556] The first stage of the pipeline expands (at 763) theJPEG-compressed contone CMYK layer, expands (at 764) the Group 4Fax-compressed bi-level black layer, and renders (at 766) the bi-levelnetpage tag layer according to the tag format defined in section 1.2,all in parallel. The second stage dithers (at 765) the contone CMYKlayer and composites (at 765) the bi-level black layer over theresulting bi-level CMYK layer. The resultant bi-level CMYK+IR dot datais buffered and formatted (at 767) for printing on the Memjet™ printhead350 via a set of line buffers. Most of these line buffers are stored inthe off-chip DRAM. The final stage prints the six channels of bi-leveldot data (including fixative) to the Memjet™ printhead 350 via theprinthead interface 768.

[0557] When several print engine controllers 760 are used in unison,such as in a duplexed configuration, they are synchronized via a sharedline sync signal 770. Only one print engine 760, selected via theexternal master/slave pin 771, generates the line sync signal 770 ontothe shared line.

[0558] The print engine controller 760 contains a low-speed processor772 for synchronizing the page expansion and rendering pipeline,configuring the printhead 350 via a low-speed serial bus 773, andcontrolling the stepper motors 675, 676.

[0559] In the 8½″ versions of the netpage printer, the two print engineseach prints 30 Letter pages per minute along the long dimension of thepage (11″), giving a line rate of 8.8 kHz at 1600 dpi. In the 12″versions of the netpage printer, the two print engines each prints 45Letter pages per minute along the short dimension of the page (8½″),giving a line rate of 10.2 kHz. These line rates are well within theoperating frequency of the Memjet™ printhead, which in the currentdesign exceeds 30 kHz.

[0560] 8 Netpage Tags

[0561] 8.1 Tag Tiling

[0562] 8.1.1 Planar Surface Tag Tiling

[0563] In order to support “single-click” interaction with a taggedregion via a sensing device, the sensing device must be able to see atleast one entire tag 4 in its field of view no matter where in theregion or at what orientation it is positioned. The required diameter ofthe field of view of the sensing device is therefore a function of thesize and spacing of the tags 4.

[0564] In the case where the tag shape is circular, such as thepreferred tag 4 described earlier, the minimum diameter m of the sensorfield of view is obtained when the tags 500, of diameter k, are tiled onan equilateral triangular grid, as shown in FIG. 52 and defined in EQ 1.This is achieved when the center-to-center tag spacing is the same asthe tag diameter k.

[0565] With a tag diameter k of 256 dots (˜4 mm at 1600 dpi), m istherefore 552 dots (˜8.8 mm). With a quiet area of 16 dots, i.e. aneffective tag diameter k of 272 dots (˜4.3 mm), m increases to 587 dots(˜9.3 mm).

[0566] When the tags 4 are moved a distance s apart, where s is at leastas large as k, then the minimum field of view is given by EQ 2.

[0567] When no overlap is desired in the horizontal direction betweensuccessive lines of tags 500, for example to make tag rendering easier,the tags must be moved apart by a minimum amount given by EQ 3. For a256-dot diameter tag, u is therefore 40 dots (˜0.6 mm at 1600 dpi).Since this exceeds the quiet area required for the tag, the quiet areacan be ignored if tag lines are rendered to not overlap.

[0568] Setting s=k+u in EQ 2 gives EQ 4. For a 256-dot diameter tag, sis therefore 296 dots (˜4.7 mm at 1600 dpi), and m is 598 dots (˜9.5mm).

[0569] 8.1.2 Spherical Surface Tag Tiling

[0570] A regular icosahedron is often used as the basis for generatingan almost regular triangular tiling of a sphere. A regular icosahedron,such as icosahedron 526 in FIG. 53, is composed of twenty equal-sizedequilateral triangular faces 528 sharing thirty edges 530 and twelvevertices 532, with five of the edges 530 meeting at each of the vertices532.

[0571] To achieve the required tiling, the icosahedron 526 is inscribedin a target sphere, and each triangle 528 of the icosahedron 526 issubdivided into an equal number of equal-sized equilateral subdivisiontriangles to yield the desired total number of triangles. If each edge530 of the icosahedron is divided into v equal intervals, defining a setof v-l points along each edge, and each pair of corresponding pointsalong any two adjacent edges is joined by a line parallel to the othershared adjacent edge, the lines so drawn intersect at the vertices ofthe desired equal-sized and equilateral subdivision triangles, resultingin the creation of v² triangles per triangular face 528 of theicosahedron 526, or 20v² triangles in all. Of the resulting 10v²+2vertices, five triangular faces meet at each of the twelve originalvertices of the icosahedron 526, and six triangular faces meet at theeach of the remaining vertices. The twelve original vertices 532 alreadylie on the sphere, while the remaining vertices lie inside the sphere.Each created vertex is therefore centrally projected onto the sphere,giving the desired tiling.

[0572] A sphere approximated by a regular polyhedron in this way isreferred to as a geodesic, and the parameter v is referred to as thefrequency of the geodesic. FIG. 54 shows an icosahedral geodesic 534with v=3, i.e. with 180 faces 528.

[0573] The closer a subdivision triangle is to the center of a face ofthe icosahedron 526, the further it is from the surface of the sphere,and hence the larger it is when projected onto the sphere. To minimisevariation in the size of projected subdivision triangles, subdivisonvertices can systematically be displaced prior to projection (Tegmark,M., “An Icosahedron-Based Method for Pixelizing the Celestial Sphere”,ApJ Letters, 470, L81, Oct. 14, 1996). If v=1 then no vertices arecreated and the angle subtended by a triangular face at a vertex remains60°. As v increases, however, the surface defined by the five triangularfaces surrounding each original vertex becomes increasingly flat, andthe vertex angle of each triangular face converges on 72° (i.e. 360°/5).This defines the worst case for a tag tiling of a sphere. In a 72°isosceles triangle the base length is 1.18 times the length of the twosides. The maximum tag spacing s for the purposes of calculating thesensor field of view is therefore close to 1.18 k. With a tag diameterof 256 dots and a quiet area of 16 dots, i.e. an effective tag diameterk of 272 dots (˜4.3 mm), m is therefore 643 dots (−10.2 mm) according toEQ 2.

[0574] The angle subtended by each edge of an icosahedron at the centerof the circumscribing sphere is given by EQ 5

[0575] For a sphere of radius r the arc length of each centrallyprojected edge is rθ. Given a tag diameter of K in the same units as r,the number of tags n required to cover the sphere is given by EQ 6.

[0576] For a given n, r is limited by EQ 7.

[0577] If n is limited to 2^(16,) to allow the use of a 16-bit tag IDwithout requiring multiple regions to cover the sphere, and K is takento be 4.3 mm as above, then r is limited to ˜310 mm.

[0578] A typical globe has a radius of 160 mm. Its projected arc lengthof =177 mm fits 41 evenly spaced tags with negligible additionalspacing. Such a globe uses 16812 tags in total.

[0579] 8.1.3 Arbitrary Curved Surface Tag Tiling

[0580] A triangle mesh can approximate a surface of arbitrary topographyand topology without introducing discontinuities or singularities, withthe local scale of the mesh being dictated by the local curvature of thesurface and an error bound. Assuming the existence of a triangle meshfor a particular surface, an effective non-regular tiling of tags can beproduced as long as each mesh triangle respects a minimum vertex angleand a minimum edge length. A tiling is considered effective with respectto a particular sensing device if the field of view of the sensingdevice is guaranteed to include at least one complete tag at anyposition of the sensing device on the surface.

[0581] The tiling procedure starts by placing a tag at each vertex ofthe mesh, so the minimum edge length is the same as the tag diameter k.The tiling procedure proceeds by inserting a tag at the midpoint of anyedge whose length exceeds a maximum tag separation s. As illustrated inFIG. 9, the maximum tag spacing s is calculated so that if two adjacenttags 4 a and 4 b are a distance s+ε apart, then there is room foranother tag 4 c between them, i.e. EQ 8.

[0582] However, if the vertex angle between two edges of length s+ε isless than 60°, then the inserted tags will overlap.

[0583] To prevent inserted tags from overlapping, a minimum tagseparation t is introduced, where t≧k. The minimum vertex angle α thenbecomes a function of k and t, as shown in EQ 9.

[0584] Clearly, when t=k, β is constrained to be 60°, i.e. the mesh isconstrained to be equilateral. But as illustrated in FIG. 56, when t>k,β can be less than 60° without inserted tags overlapping.

[0585] The maximum tag separation s must be based on the new minimum tagseparation t, in accordance with EQ 10.

[0586] When considering a particular mesh triangle, there are fourdistinct tag insertion scenarios. By assuming that the minimum vertexangle is no less than 30° (i.e. half of 60°), it can be shown thatwhenever a mesh triangle has at least one edge less than or equal to sin length, the remaining two edges are less than 2s in length. Inpractice the minimum vertex angle is typically at least 45°.

[0587] In the first scenario (FIG. 57) no edges of a triangle 546 exceeds in length, so the tagging of the triangle is already complete.

[0588] In the second scenario (FIG. 58) one edge 548 of a triangle 550exceeds s in length. A tag 552 is inserted at the midpoint of the edge548 to complete the tagging of the triangle 550.

[0589] In the third scenario (FIG. 59) two edges 554, 556 of a triangle558 exceed s in length. Tags 560, 562 are inserted at the midpoint ofeach of the two long edges 554, 556 and this may complete the tagging ofthe triangle 558. Centers of the two inserted tags 560, 562 togetherwith the two vertices 564, 566 of the short edge 568 of the originaltriangle 558 form a trapezoid. If either diagonal of the trapezoidexceeds s in length then a final tag 570 is inserted at the center ofthe trapezoid to complete the tagging of the triangle.

[0590] In the fourth scenario (FIG. 60) all three edges 572 of atriangle 573 exceed s in length. A tagged vertex 574 is inserted at themidpoint of each edge 572 and the three new vertices 574 are joined byedges 576. The tagging procedure is then recursively applied to each ofthe four resultant triangles 577, 578, 579 and 580. Note that the newtriangles respect the minimum vertex angle because they have the sameshape as the original triangle 573.

[0591] The tag tiling variables are summarized in Table 4. TABLE 4 Tagtiling variables variable Meaning β minimum vertex angle k tag diameterm minimum diameter of sensor field of view on surface s maximumcenter-to-center tag spacing t minimum center-to-center tag spacing

[0592] 8.2 Tag Sensing

[0593] 8.2.1 Pen Orientation

[0594] To allow a pen-like sensing device to be used as a comfortablewriting instrument, a range of pen orientations must be supported. Sincethe pen nib is constrained to be in contact with the surface, theorientation of the pen can be characterized by the yaw (z rotation),pitch (x rotation) and roll (y rotation) of the pen, as illustrated inFIG. 61. While the yaw of the pen must be unconstrained, it isreasonable to constrain the pitch and roll of the pen as well as theoverall tilt of the pen resulting from the combination of pitch androll.

[0595] Yaw is conventionally applied after pitch, such that, forexample, in the case of a pen device it would define a twist about thephysical axis rather than a direction in the surface plane. In a penwith a marking nib, however, the image sensor is mounted off the axis ofthe pen and the pen's image sensing ability (and hence its yaw sensingability) is therefore constrained unless the pen is held almostvertically, as discussed below. Yaw is therefore applied before pitch,allowing the full yaw range to be specified by rotating the pen relativeto the surface while keeping pitch and roll constant.

[0596] Pitch and roll are conventionally defined as y and x rotations,respectively. Here they are defined as x and y rotations, respectively,because they are defined with respect to the x-y coordinate system ofthe surface, where the y axis is the natural longitudinal axis and the xaxis is the natural lateral axis when viewed by a user. In aright-handed 3D coordinate system, roll is conventionally defined aspositive when anticlockwise, while pitch and yaw are conventionallydefined as positive when clockwise. Here all rotations are defined aspositive when anticlockwise.

[0597] The pen's overall tilt (θ) is related to its pitch (φ) and theroll (ψ) in accordance with EQ 11.

[0598] The pen's tilt affects the scale at which surface features areimaged at different points in the field of view, and therefore affectsthe resolution of the image sensor. Since it is impractical to sense thearea directly under the pen nib, the pen's tilt also affects thedistance from the nib to the center of the imaged area. This distancemust be known to allow a precise nib position to be derived from theposition determined from the tag.

[0599] 8.2.2 Image Sensing

[0600] The field of view can be modeled as a cone defined by a solidhalf-angle α (giving an angular field of view of 2α), and an apex heightof D above the surface when the optical axis is vertical. Although theimage sensor is typically rectangular, only the largest ellipticalsubarea of the image sensor is relevant to guaranteeing that asufficiently large part of the surface is imaged, as quantified earlier.

[0601] The intersection of the field of view cone with the surfacedefines an elliptical window on the surface. This window is circularwhen the optical axis is vertical.

[0602]FIG. 62 illustrates the geometric relationship, for a givenpitch-related tilt θ of the pen's optical axis, between the pen's nib(point A), the pen's optical axis (CE), and the field of view window(FH). The tilt is defined to be clockwise positive from the vertical.The equations which follow apply to both positive and negative tilt.

[0603] When the pen is not tilted, the window diameter (i.e. |BD|) isgiven by EQ 12.

[0604] If, when the pen is not tilted, the distance from the nib to edgeof the window (i.e. |AB|) is T, then the distance S from the nib to thecenter of the window (i.e. |AC|) is given by EQ 13.

[0605] When the pen is tilted by θ, the distance from the viewpoint tothe surface along the optical axis is reduced to d (i.e. |GE|), given byEQ 14.

[0606] The width of the window (i.e. |FH|) is then given by EQ 15.

[0607] D and α must be chosen so that an adequately large area is imagedthroughout the supported tilt range. The required minimum diameter m ofthe area is given by EQ 4, while the width of the actual imaged area isgiven by EQ 15. This then gives EQ 16.

[0608] Once D and α are determined, an image sensor resolution must bechosen so that the imaged area is adequately sampled, i.e. that themaximum feature frequency is sampled at its Nyquist rate or higher.

[0609] When imaged, the scale of the surface decreases with increasingdistance from the viewpoint and with increasing inclination relative tothe viewing ray. Both factors have maximum effect at point F forpositive tilt and point H for negative tilt, i.e. at the point in thewindow furthest from the viewpoint. Note that references to F in thefollowing discussion apply to H when the tilt is negative.

[0610] The distance of point F from the viewpoint (i.e. |EF|) is givenby EQ 17.

[0611] Scaling due to the inclination of the surface relative to theviewing ray through F (EF) is given by EQ 18.

[0612] If the surface feature frequency is f then the angular surfacefeature frequency ω at F (i.e. with respect to the field of view) due toboth factors is given by EQ 19.

[0613] When there is no object plane tilt (i.e. θ=0), this reduces to EQ20.

[0614] The image sensor is, by definition, required to image at leastthe entire angular field of view. Since the pixel density of the imagesensor is uniform, it must image the entire field of view at maximumfrequency. Given an angular field of view in image space of 2α′, animage sensor tilt (i.e. image plane tilt) with respect to the opticalaxis of θ′, and a sampling rate of n (where n≧2 according to Nyquist'stheorem), the minimum image sensor resolution q is given by EQ 21 and EQ22.

[0615] The cos-squared term in the numerator in EQ 22 results from thesame reasoning as the cos-squared term in the denominator in EQ 19.

[0616] When there is no image plane tilt (i.e. θ=0), and the image spaceand object space angular fields of view are equal (i.e. α′=α), thisreduces to EQ 23 and EQ 24.

[0617] When there is no object plane tilt (i.e. θ=0) this reducesfurther to EQ 25.

[0618] When the image plane tilt and the object plane tilt are equal(i.e. θ′=0), and the image space and object space angular fields of vieware equal (i.e. α′=α), EQ 22 reduces to EQ 26.

[0619] Matching the image plane tilt to the object plane tilt thereforeyields a smaller required image sensor size than when the image sensortilt is fixed at zero, and eliminates perspective distortion from thecaptured image. Variable image sensor tilt is, however, a relativelycotly option in practice, and also requires greater depth of field.

[0620]FIG. 63 illustrates the geometric relationship, for a givenroll-related tilt θ of the pen's optical axis, between the pen's nib(point A), the pen's optical axis (CE), and the field of view window(FH). The tilt is again defined to be clockwise positive from thevertical. With the exception of EQ 13, the preceding equations applyequally to roll-induced tilt. For roll-induced tilt the distance S fromthe nib to the center of the window (i.e. |AC|) is zero rather than asdefined by EQ 13.

[0621] For pitch-induced tilt, the magnitude of the tilt range ismaximised by choosing a minimum (negative) tilt and a maximum (positive)tilt which have the same image sensor requirement. Since, forpitch-induced tilt, the surface is more distant for negative tilt thanfor positive tilt of the same magnitude, the minimum has a smallermagnitude than the maximum. For roll-induced tilt they have the samemagnitude.

[0622] As described above, the smallest features of the tag 4 are thestructures which encode the data bits, and these have a minimum diameterof 8 dots. This gives a maximum feature frequency f of about 7.9 per mmat 1600 dpi.

[0623] As calculated according to EQ 4 above, an equilateral triangulartiling of 256-dot diameter tags with no overlap between successive linesof tags requires a minimum field of view window diameter on the surfaceof 598 dots, or about 9.5 mm at 1600 dpi.

[0624] Most people hold a pen at about +30° pitch and 0° roll. Theinking ball of a ball-point nib loses effective contact with the surfacebeyond about +50° pitch (i.e. 40° from the horizontal). A reasonabletarget pitch range is therefore −100 to +50°, and a reasonable rollrange −30° to +30°, bearing in mind greater limitations on combinedpitch and roll as given by EQ 11.

[0625] The highly compact (1.5 mm²) Matsushita CCD image sensor(Matsushita Electronic Corporation, and is described in a paper byItakura, K T Nobusada, N Okusenya, R Nagayoshi, and M Ozaki, “A 1 mm50k-Pixel IT CCD Image Sensor for Miniature Camera System”, IEEETransactions on Electronic Devices, Volt 47, number 1, January 2000) issuitable for use in a compact device such as a pen. It has an availableresolution of 215×215 pixels. Assuming equal image and object spaceangular fields of view, no image plane tilt, and a nib-to-windowdistance T of 4 mm′ optimizing the geometry using EQ 16 and EQ 24 toachieve the desired pitch and roll ranges stated above yields a pitchrange of −16° to +48° (64°) and a roll range of −28° to +28° (56°) witha viewing distance D of 30 mm and an angular field of view of 18.8°(α=9.4°). The available pitch range is actually −21° to +43°, and thisis mapped to close to the desired range by pitching the optical axis at−5° relative to the physical axis. Note that the tilt range can beexpanded slightly by optimizing a non-zero tilt of the image plane.

[0626] The overall pen tilt is thus confined to an elliptical cone whosemajor angle is 64° in the pitch plane and whose minor angle is 56° inthe roll plane.

[0627] The image sensing variables are summarized in Table 5. TABLE 5Image sensing variables variable meaning α Object space field of viewhalf-angle α′ Image space field of view half-angle γ Pen yaw θ Objectplane tilt (i.e. overall pen tilt) θ′ Image plane tilt φ Pen pitch ψ Penroll ω Angular frequency in field of view D Normal viewing distance dTilted viewing distance f Surface feature frequency n Sampling rate qImage sensor resolution S Distance from nib to center of field of viewon surface (when θ = 0) T Distance from nib to edge of field of view onsurface (when θ = 0)

[0628] 8.3 Tag Decoding

[0629] 8.3.1 Tag Image Processing and Decoding

[0630] Tag image processing is described earlier in Section 1.2.4. Itculminates in knowledge of the 2D perspective transform on the tag, aswell as the decoded tag data.

[0631] 8.3.2 Inferring the Pen Transform

[0632] Once the 2D perspective transform is obtained which accounts forthe perspective distortion of the tag in the captured image, asdescribed earlier, the corresponding discrete 3D tag transform withrespect to the pen's optical axis can be inferred, as described below inSection 8.4.

[0633] Once the discrete 3D tag transform is known, the corresponding 3Dpen transform can be inferred, i.e. the transform of the pen's physicalaxis with respect to the surface. The pen's physical axis is the axiswhich is embodied in the pen's shape and which is experienced by thepen's user. It passes through the nib. The relationship between thephysical axis and the optical axis is illustrated in FIG. 64.

[0634] It is convenient to define three coordinate spaces. In sensorspace the optical axis coincides with the z axis and the the viewpointis at the origin. In pen space the physical axis coincides with the zaxis and the nib is at the origin. In tag space the tag 4 lies in thex-y plane with its center at the origin. The tag transform transformsthe tag 4 from tag space to sensor space.

[0635] Sensor space is illustrated in FIG. 64. The labelling of pointsin FIG. 64 is consistent with the labelling in FIG. 62. The viewpoint isat E, the sensed point is at G, and the nib is at A. The intersectionpoint G between the optical axis and the surface is referred to as thesensed point. In contrast with the geometry illustrated in FIG. 62 wherethe nib is considered as a point, here the nib is considered as a smallsphere. If the nib is curved, then the tilt of the physical axis affectsthe offset between the sensed point and the contact point between thenib and the surface. The center point K of the spherical nib, aboutwhich the physical axis pivots, is referred to as the pivot point.

[0636] The nib makes nominal contact with the surface at point A whenthe optical axis is vertical. KA is defined to be parallel to theoptical axis. When the pen is tilted, however, contact is at point L, asshown in FIG. 65. Given the radius R of the nib, the distance of thepivot point K from the surface, e.g. at A or L, is always R.

[0637] The discrete tag transform includes the translation of the tagcenter from the sensed point, the 3D tag rotation, and the translationof the sensed point from the viewpoint.

[0638] Given the translation d of the sensed point from the viewpoint inthe discrete tag transform, and according to EQ 14, the sensed point isgiven by EQ 27.

[0639] Since the physical axis only differs from the optical axis by a ytranslation and x rotation (i.e. pitch), the physical axis lies in they-z plane. With reference to FIG. 64, where |AC|=S and |EC|=D (just asin FIG. 62), it is clear that in sensor space the position of the pivotpoint is given by EQ 28.

[0640] The vector from the sensed point to the pivot point is thereforegiven by EQ 29.

[0641] The vector from the pivot point to the contact point is bydefinition a surface normal of length R. It is constructed by applyingthe 3D tag rotation M to a tag space surface normal, normalizing theresult, and scaling by R, as shown in EQ 30 and EQ 31.

[0642] The vector from the sensed point to the contact point is thenobtained in accordance with EQ 32.

[0643] This is transformed into tag space by applying the inverse of thetag transform 3D rotation, and is then added to the vector from the tagcenter to the sensed point, to yield the vector from the tag center tothe contact point in tag space, i.e. on the surface, in accordance withEQ 33.

[0644] This is finally added to the tag's absolute location, as impliedby its tag ID, to yield the nib's desired absolute location in thetagged region: see EQ 34.

[0645] The final step is to infer the pen's 3D orientation from thetag's 3D orientation. The pen's discrete rotations are simply theinverses of the tag's discrete rotations, with the pen's pitch alsoincluding the effect of the pitch (φ_(sensor)) of the optical axis withrespect to the pen's axis, as defined in EQ 35, EQ 36 and EQ 37.

[0646] 8.4 Inferring the Tag Transform

[0647] The image of the tag 4 captured by the image sensor containsperspective distortion due to the position and orientation of the imagesensor with respect to the tag. Once the perspective targets of the tagare found in image space, an eight-degree-of-freedom perspectivetransform is inferred based on solving the well-understood equationsrelating the four tag-space and image-space point pairs. The discretetransform steps which give rise to the image of the tag are concatenatedsymbolically, and a set of simultaneous non-linear equations is obtainedby equating corresponding terms in the concatenated transform and theperspective transform. Solving these equations yields the discretetransform steps, which include the desired tag offset from the nib, 3Dtag rotation, and viewpoint offset from the surface.

[0648] 8.4.1 Modeling the Tag Transform

[0649] The transform of the tag 4 from tag space to image space can bemodeled as a concatenation of the following transform steps:

[0650] x-y translate (by tag-to-viewpoint offset)

[0651] z rotate (by tag yaw)

[0652] x rotate (by tag pitch)

[0653] y rotate (by tag roll)

[0654] z translate (by tag-to-viewpoint offset)

[0655] perspective project (with specified focal length)

[0656] x-y scale (to viewport size)

[0657] These are concatenated symbolically to produce a single transformmatrix which effects the tag transform. Table 7 summarizes the discretetransform variables used in the following sections, together with therange of each variable. TABLE 7 Discrete transform variables and theirranges Vari- Unit able Abbrev. Meaning transform Range γ — yaw 0 0 ≦ γ ≦2π φ — pitch 0 −π/2 < φ < π/2 ψ — roll 0 −π/4 < ψ < π/4 t_(x) Atag-to-viewpoint x offset 0 — t_(y) B tag-to-viewpoint y offset 0 — cosγC cosine of yaw 1 −1 ≦ C ≦ 1 sinγ D sine of yaw 0 −1 ≦ D ≦ 1 cosφ Ecosine of pitch 1 0 < E ≦ 1 sinφ F sine of pitch 0 −1 < F < 1 cosψ Gcosine of roll 1 0 < G ≦ 1 sinψ H sine of roll 0 −1 < H < 1 t_(z) Itag-to-viewpoint z offset — I < 0 1/λ J inverse focal length — J > 0 S —viewport scale — S > 0

[0658] Translate in x-y plane by t_(x) and t_(y) according to EQ 42(where A=t_(x) and B=t_(y)).

[0659] Rotate about z by γ according to EQ 43 (where C=cos(γ) andD=sin(γ)), giving EQ 44.

[0660] Rotate about x by φ according to EQ 45 (where E=cos(φ) andF=sin(φ)), giving EQ 46.

[0661] Rotate about y by ψ according to EQ 47 (where G=cos(ψ) andH=sin(ψ)), giving EQ 48, where K and L are defined by EQ 49 and EQ 50.

[0662] Translate in z by t_(z) according to EQ 51 (where I=t_(z)),giving EQ 52.

[0663] Perspective project with focal length λ and projection plane atz=0 according to EQ 53 (where J=1λ), giving EQ 54.

[0664] Scale to viewport by S according to EQ 55, giving EQ 56.

[0665] Transform a point in the x-y plane (z=0) according to EQ 57,giving EQ 58.

[0666] Finally, expand K and L, giving EQ 59.

[0667] 8.4.2 2D Perspective Transform

[0668] Given an inferred eight-degree-of-freedom 2D perspectivetransform matrix as defined in EQ 60, multiply by an unknown i to obtainthe general nine-degree-of-freedom form of the matrix, as shown in EQ61.

[0669] Transform a 2D point according to EQ 62, giving EQ 63.

[0670] 8.4.3 Inferring the Tag Transform

[0671] 8.4.3.1 Equating Coefficients

[0672] Equating the coefficients in EQ 59 with the coefficients in EQ 63results in EQ 64 to EQ 72, being nine non-linear equations in 11unknowns.

[0673] These equations are augmented as required by the trigonometricidentity relating the sine and cosine of an angle (i.e. the sine andcosine of any one of yaw, pitch and roll), as shown in EQ 73.

[0674] Given the sine and cosine of an angle, the corresponding angle isobtained using a two-argument arctan as shown in EQ 74.

[0675] 8.4.3.2 Solving for X-Y Offset

[0676] EQ 66 can be simplified using EQ 64 and EQ 65 to give EQ 75 andthen EQ 76.

[0677] EQ 69 can be simplified using EQ 67 and EQ 68 to give EQ 77 andthen EQ 78.

[0678] EQ 72 can be simplified using EQ 70 and EQ 71 to give EQ 79 andthen EQ 80.

[0679] EQ 76 can be re-written as EQ 81, and EQ 78 can be re-written asEQ 82.

[0680] Equating EQ 81 and EQ 82 and solving for B yields EQ 83 throughEQ 85 and finally EQ 86, which defines B.

[0681] Substituting the value for B into EQ 82 and simplifying yields EQ87 through EQ 90 and finally EQ 91, which defines A.

[0682] This therefore gives the x-y offset of the tag 4 from theviewpoint, since A=t_(x) and B=t_(y).

[0683] 8.4.3.3 Solving for Pitch

[0684] From EQ 68, EQ 92 can be obtained.

[0685] From EQ 67, EQ 93 can be obtained.

[0686] From EQ 64, EQ 92 and EQ 93, EQ 94 can be obtained.

[0687] From EQ 65, EQ 92 and EQ 93, EQ 95 can be obtained.

[0688] From EQ 70, EQ 92 and EQ 93, EQ 96 can be obtained.

[0689] From EQ 71, EQ 92 and EQ 93, EQ 97 can be obtained.

[0690] From EQ 94, EQ 98 can be obtained.

[0691] From EQ 95, EQ 99 can be obtained.

[0692] From EQ 96, EQ 100 can be obtained.

[0693] From EQ 97, EQ 101 can be obtained.

[0694] From EQ 98 and EQ 99, EQ 102 and then EQ 103 can be obtained.

[0695] From EQ 100 and EQ 101, EQ 104 and then EQ 105 can be obtained.

[0696] From EQ 103 and EQ 105, EQ 106 and then EQ 107 can be obtained.

[0697] EQ 107 only has a valid basis if G and H are both non-zero. Since|ψ|<π/2, the cosine (G) of the roll is always positive and hencenon-zero. The sine of the roll (H) is only non-zero if the roll isnon-zero. Specific handling for zero pitch and roll is described inSection 6.7.3.10.

[0698] This therefore gives the magnitude of the sine of the pitch,since F=sin(φ), and hence the cosine (E) of the pitch by EQ 73,according to EQ 108.

[0699] Since |φ|<π/2, the cosine (E) of the pitch is always positive, sothere is no ambiguity when taking the square root. The sign of the sine(F), however, must be determined by other means, as described in Section6.7.3.9.

[0700] Given E and F, the pitch is then obtained, according to EQ 109.

[0701] 8.4.3.4 Solving for Roll

[0702] From EQ 103, EQ 110 can be obtained.

[0703] From EQ 73, EQ 111 and then EQ 112 can be obtained.

[0704] This therefore gives the magnitude of the sine of the roll, sinceH=sin(ψ), and hence the cosine (G) of the roll by EQ 73, according to EQ113.

[0705] Since |ψ<π/4, the cosine (G) of the roll is always positive, sothere is no ambiguity when taking the square root. The sign of the sine(H), however, must be determined by other means, as described in Section6.7.3.9.

[0706] Given G and H, the roll is then obtained according to EQ 114.

[0707] 8.4.3.5 Solving for Yaw

[0708] From EQ 73, EQ 92 and EQ 93, EQ 115 and then EQ 116 can beobtained.

[0709] From EQ 92 and EQ 116, EQ 117 and then EQ 118 can be obtained.

[0710] From EQ 92 and EQ 116, EQ 119 and then EQ 120 can be obtained.

[0711] In EQ 116, and hence EQ 118 and EQ 120, the sign of the squareroot is determined by the sign of i, which can be determined from EQ 80,giving EQ 121.

[0712] Since I (t_(z)) is negative, J (1/λ) is positive, and IJ<−1(because |t_(z)|>λ), then EQ 122 holds.

[0713] Given C and D, the yaw is then obtained according to EQ 123.

[0714] 8.4.3.6 Solving for Viewport Scale

[0715] The cosine (C) and sine (D) of the yaw are by definition neversimultaneously zero. Since the cosine (E) of the pitch is never zero,either EQ 67 or EQ 68 can therefore always be used to determine theviewport scale (S).

[0716] If D is non-zero, then from EQ 67, EQ 124 can be obtained.

[0717] Otherwise, if C is non-zero, then from EQ 68, EQ 125 can beobtained.

[0718] 8.4.3.7 Solving for Focal Length

[0719] Similarly, since the cosine (G) of the roll is never zero, eitherEQ 70 or EQ 71 can be used to determine the inverse focal length (J), solong as either the pitch or roll is non-zero. However, the signs of thesines (F and H) of the pitch and roll may not be known. However, thesign of the product (FH) of the sines of the pitch and roll is given byEQ 103, as shown in EQ 126.

[0720] The sign can be assigned arbitrarily to F, since the sign of J isknown a priori. If gi is non-zero, then from EQ 70, EQ 127 can beobtained.

[0721] If hi is non-zero, then from EQ 71, EQ 128 can be obtained.

[0722] In practice, the choice between using EQ 127 and EQ 128 is basedon which of gi and hi has the larger magnitude. The inverse focal lengthis unknown if gi and hi are both zero, i.e. if the pitch and roll areboth zero.

[0723] 8.4.3.8 Solving for Z Offset

[0724] Once the inverse focal length (J) is known, the z offset (I) isobtained from EQ 80, according to EQ 129.

[0725] Again, the z offset (I) is unknown if the inverse focal length(J) is unknown, i.e. if the pitch and roll are both zero.

[0726] 8.4.3.9 Determining Direction of Pitch and Roll

[0727] The sign of the product (FH) of the sines of the pitch and rollis given by EQ 126. Since −π/4 <ψ<π/4, a roll adjustment of +π/4 can beintroduced to ensure the roll is always positive, without invalidatingany other assumptions. Once the roll adjustment is introduced, EQ 126gives the sign of the sine (F) of the pitch alone.

[0728] The roll adjustment is introduced as follows. The viewport scale(S), inverse focal length (J), and z offset (I) are all computed asdescribed. A 3D transform matrix is created from the 2D perspectivetransform matrix. The inverses of the viewport scale, focal lengthprojection and z translation are applied to the 3D matrix in reverseorder. The roll adjustment is then applied by pre-multiplying the matrixby a π/4 y rotation matrix. The roll, pitch and yaw are computed asdescribed. Since the roll is positive, the pitch direction is now known.The π/4 roll adjustment is finally subtracted from the roll to give theactual roll.

[0729] When the roll and pitch are both zero, the focal length and zoffset are both unknown as described above. However, in this case thereis no need to adjust the roll since the pitch and roll are alreadyknown.

[0730] 8.4.3.10 Handling Zero Pitch and Roll

[0731] When either the pitch or roll is zero, the general solution basedon EQ 107 becomes invalid. The table of FIG. 85 shows the 12 degenerateforms of EQ 64 through EQ 71 which result when the yaw is variously zero(or π), π/2 (or 3π/2), and non-zero, and the pitch and roll arevariously zero and non-zero. The table of FIGS. 86 and 87 sets out therequired logic for detecting and handling cases where the pitch and/orroll are zero, with each case motivated by zeros appearing in the tableof FIG. 85. The cases in the table of FIG. 85 are labelled with the casenumbers from the table of FIGS. 86 and 87.

[0732] CONCLUSION

[0733] The present invention has been described with reference to apreferred embodiment and number of specific alternative embodiments.However, it will be appreciated by those skilled in the relevant fieldsthat a number of other embodiments, differing from those specificallydescribed, will also fall within the spirit and scope of the presentinvention. Accordingly, it will be understood that the invention is notintended to be limited to the specific embodiments described in thepresent specification, including documents incorporated bycross-reference as appropriate. The scope of the invention is onlylimited by the attached claims.

1. A region defined in relation to a surface, coded data being disposedwithin the region, wherein the coded data includes identity data foridentifying the region and wherein the coded data comprises a pluralityof substantially undifferentiated marks positioned relative to a set ofpredetermined nominal mark positions.
 2. A region according to claim 1,wherein each mark represents one of a plurality of coded values.
 3. Aregion according to claim 2, wherein the coded value represented by amark is at least partially determined by the position of the markrelative to the set of predetermined nominal mark positions.
 4. A regionaccording to claim 1 wherein the predetermined nominal mark positionsare arranged relative to a plurality of nominal lines.
 5. A regionaccording to claim 4 wherein at least one pair of the lines are spacedapart from one another by a distance of less than 100 millimeters.
 6. Aregion according to claim 1, wherein the marks have centers and whereinthe relative spacing of the centers of at least one pair of adjacentmarks is less than 12 millimeters.
 7. A region according to claim 1,wherein each mark has a minimum radius and a maximum radius and whereinthe length of a mark's minimum radius is greater than 40% of the lengthof that mark's maximum radius.
 8. A region according to claim 1, whereinany 10 millimeter diameter subregion of the region includes sufficientcoded data to identify the region.
 9. A region according to claim 1,wherein the coded data is also indicative of a plurality of referencepoints of the region and wherein any 10 millimeter diameter subregion ofthe region includes sufficient information to identify at least onereference point of the region.
 10. A surface, including a regionaccording to any one of the preceding claims.
 11. A method of producinga surface having a region, the method including the steps of: (a)defining coded data as a plurality of substantially undifferentiatedmarks positioned relative to a set of predetermined nominal markpositions, the coded data being indicative of a region identityassociated with the region; and (b) disposing the coded data within theregion on the surface.
 12. A method according to claim 11, wherein eachmark represents one of a plurality of coded values.
 13. A methodaccording to claim 12, wherein the coded value represented by a mark isat least partially determined by the position of the mark relative tothe set of predetermined nominal mark positions.
 14. A method accordingto claim 11 wherein the predetermined nominal mark positions arearranged relative to a plurality of nominal lines.
 15. A methodaccording to claim 14 wherein at least one pair of the lines are spacedapart from one another by a distance of less than 100 millimeters.
 16. Amethod according to claim 11, wherein the marks have centers and whereinthe relative spacing of the centers of at least one pair of adjacentmarks is less than 12 millimeters.
 17. A method according to claim 11,wherein each mark has a minimum radius and a maximum radius and whereinthe length of a mark's minimum radius is greater than 40% of the lengthof that mark's maximum radius.
 18. A method according to claim 11,wherein any 10 millimeter diameter subregion of the region includessufficient coded data to identify the region.
 19. A method according toclaim 11, wherein the coded data is also indicative of a plurality ofreference points of the region and wherein any millimeter diametersubregion of the region includes sufficient information to identify atleast one reference point of the region.